Veterinarian Terminology

Veterinarian Terminology

The Egyptian Papyrus of Kahun (Twelfth Dynasty of Egypt) is the first extant record of veterinary medicine. The Shalihotra Samhita, dating from the time of Ashoka, is an early Indian veterinary treatise. The edicts of Asoka read: “Everywhere King Piyadasi (Asoka) made two kinds of medicine (चिकित्सा) available, medicine for people and medicine for animals. Where there were no healing herbs for people and animals, he ordered that they be bought and planted. – Origins of Neuroscience: A History of Explorations Into Brain Function



abdomen – The middle section of the body, between the chest and the pelvis.
abdominal cavity – The body cavity between the chest and the pelvis.
abdominocentesis – Surgical procedure in which a needle is inserted into the abdomen to withdraw fluid.
abortion – The end of a pregnancy before the expelled fetus can survive independently, either by spontaneous abortion (miscarriage) or by a medical termination of pregnancy.
abscess – A pocket of pus, usually caused by a bacterial infection.
acariasis – Disease caused by a mite of the order Acarina.
acaricide – A chemical agent used to kill mites.
ACE inhibitor – Any of a class of drugs intended to lower blood pressure by widening blood vessels. ACE stands for angiotensin-converting enzyme.
acidic – A liquid that has a pH lower than 7.
acquired – Conditions that are not inborn and that develop during the animal’s life.
acromegaly – A disorder of excessive growth hormone secretion by the pituitary gland, resulting in excessive growth of bones in the legs.
actinobacillosis – Disease caused by bacteria of the genus Actinobacillus.
actinomycosis – A bacterial infection in humans, swine, and cattle that causes hard masses to form in the mouth and jaw.
acupuncture – A procedure adapted from Chinese medical practice in which specific body areas are pierced with fine needles for therapeutic purposes.
acute – A condition that has a brief or short course; signs often develop suddenly and may be severe.
acute pain – The short-term sharp, throbbing, aching, or burning sensation in response to a stimulus (twisting, crushing, or burning) or tissue injury (bruises, wounds, and surgical incisions).
Addison’s disease – A deficiency of adrenal gland hormones.
adenocarcinoma – A malignant tumor formed in the epithelium, or covering tissue, of an organ.
adenoma – A benign tumor formed in glandular tissue.
adenovirus – A virus of the family Adenoviridae.
adrenal gland – A small, paired gland located near the kidneys that produces cortisol, epinephrine, and other hormones.
aerosol – A suspension of particles dissolved in liquid and dispersed in a fine mist.
aflatoxicosis – Poisoning caused by consumption of foods contaminated with a toxin produced by the fungus Aspergillus flavus.
African horse sickness – An equine viral disease that is widespread in Africa. It is characterized by signs of lung and blood system impairment, and is most frequently transmitted by midges or mosquitoes.
agalactia – Partial or complete lack of milk flow from the mammary gland.
agent – Anything that produces an effect. For example, viruses and bacteria are agents that cause disease.
aggression – Behavior that is related to conflict between individuals; includes both threats and attacks.
agonist – A drug or other chemical that can bind to a receptor or cell to trigger a response typical of a naturally occurring substance.
agouti – A mottled coat color in rodents, characterized by fur with bands of different colors.
airway – Passage for air from the nose or mouth to the lungs.
algal poisoning – A toxic and often deadly condition caused by heavy growths of blue-green algae in drinking water.
alkaline – A substance with a pH higher than 7; also referred to as basic.
alkaloidosis – Poisoning by alkaloids, plant toxins that damage the liver.
allergy – An abnormally high sensitivity to certain substances, such as pollens, foods, or microorganisms.
alloimmune reaction – A type of immune reaction that occurs when the body produces antibodies against the tissues of another animal. This may occur, for example, when one animal receives a blood transfusion from another animal of the same species but with a different blood type.
alopecia – A partial or complete loss of hair in areas where it is usually found.
alternative therapy – Therapy used instead of conventional treatments (for example, homeopathic treatment).
alveoli – Plural form of the word alveolus.
alveolus – Tiny air-holding sac formed at the end of air passageways in the lungs, where the barrier between the air and the blood is a thin membrane.
amino acid – A chemical compound that forms the basic building block of proteins.
amoeba – A type of protozoa, or single-celled organism. Some are parasitic and can cause infection in animals.
amphetamine – A class of drugs that stimulates the central nervous system and the cardiovascular system.
amphibian – A class of cold-blooded animals that spends at least part of their life cycle living in water.
amputation – The removal of a limb or other part of the body.
amyloid – A type of abnormally folded protein that may collect in various body tissues and interfere with their function.
amyloidosis – Disease characterized by accumulation of abnormal protein deposits.
anabolic – Pertaining to a metabolic process in which complex molecules are created from simpler ones.
analgesia – Treatment given to control pain; a deadening or absence of the sense of pain without loss of consciousness.
analgesic – A class of drugs that relieve pain.
anaphylactic shock – A rare, life-threatening, immediate allergic reaction to something that has entered the body, such as food, an injection, or an insect sting. Also called anaphylaxis.
anemia – An abnormally low red blood cell count caused by insufficient intake of iron in the diet, blood loss, or other medical conditions.
anesthesia – A lack of all sensation, particularly sensitivity to pain. It can be induced medically or result from trauma, and it can be limited to a small area (local anesthesia) or affect the entire body (general anesthesia).
anesthetic – An agent used to induce anesthesia, including injectable drugs and inhaled gases.
anestrus – An interval of sexual inactivity between 2 periods of estrus in female mammals that breed cyclically.
aneurysm – A dilation or bulging of a blood vessel caused by a weakening of its walls.
animal-assisted therapy – Using animals as therapy for the sick or elderly in nursing or other rehabilitation centers because of the positive effect such visits have on residents and patients.
animal welfare – Human efforts to reduce and prevent pain and suffering and promote well-being in animals.
anorexia – A lack or loss of appetite.
anoxia – Lack of oxygen in the blood or body tissues.
antacid – A medication that neutralizes acidity, especially in the stomach.
antagonist – A drug or substance that nullifies the effect of another substance.
anterior – Located toward the head or the front end of the body.
anterior uvea – Part of the front portion of the eye, including the iris and ciliary body.
anthelmintic – A class of drugs used to treat infection with parasitic worms.
anthrax – An often-fatal infectious disease caused by Bacillus anthracis bacteria that may infect all warm-blooded animals, including humans.
antibacterial – Destroying or inhibiting the growth of bacteria.
antibiotic – A class of drugs used to destroy bacteria while remaining safe for the human or animal being treated.
antibiotic resistance – Ability of a microorganism (such as bacteria) to resist the effects of an antibiotic drug.
antibody – A molecule produced by the immune system that attacks a particular foreign substance (antigen) in the body.
anticholinergic – A class of drugs that block acetylcholine receptors in nerves.
anticoagulant – A substance that stops blood from clotting.
anticonvulsant – A class of drugs used to prevent or relieve convulsions.
antidepressant – A class of drugs designed to relieve depression in humans; may also be used to help control behavior problems in pets.
antidote – A substance that counteracts the effect of a poison or toxin.
antiemetic – One of a group of drugs used to retard or stop vomiting.
antifungal – A class of drugs that destroy or prevent the growth of fungi.
antigen – Any substance that can stimulate an immune response.
antihistamine – A class of drugs used to relieve allergy signs by blocking the inflammatory action of histamines.
anti-inflammatory – Medication that prevents or reduces inflammation.
antimicrobial – A large group of drugs used to fight infections caused by bacteria, fungi, and viruses.
antineoplastic – A group of chemical agents or drugs used to combat cancer.
antioxidant – A substance that inhibits oxidation of other compounds.
antiparasitic – Any of a group of drugs used to combat infestation with parasites.
antiseptic solution – A solution of a substance that kills or inhibits the growth of microbes.
antitoxin – A compound that neutralizes a specific toxin.
antivenin – An antidote to a particular venom; a serum that counteracts venom.
antiviral – Compound that kills or inhibits the growth of viruses.
anus – The opening at the end of the intestinal tract where solid wastes are pushed out of a body.
aorta – The largest artery in the body. It carries blood away from the heart on its way to distribute oxygen to all body tissues except the lungs.
aortic arch – The curved portion between the ascending and descending portions of the aorta.
aortic valve – A heart valve comprising 3 flaps that controls the flow of blood from the left ventricle into the aorta.
aplasia – Incomplete or incorrect development of a body part.
aquatic – Describes organisms that live in water.
arboreal – Describes species that spend most or all of their lives in trees.
arrhythmia – An abnormal pattern of contraction of the heart, caused by a disturbance in conduction of the normal electrical impulses within the heart.
arsenical – A substance (a drug or insecticide) containing arsenic.
arterial dilator – A drug that dilates the small arteries, making it easier for the heart to pump blood away from itself.
artery – Blood vessel that carries oxygen-rich blood away from the heart and toward the body’s tissues.
arthritis – Inflammation of a joint; often characterized by swelling, pain, and redness.
arthroscopy – Examination of the interior of a joint, such as the knee, using a type of endoscope that is inserted into the joint through a small incision.
artificial insemination – Introduction (with a syringe or other device) of semen into the uterus without sexual contact.
ascarid – A class of roundworms whose larvae can cause disease.
ascites – A condition in which fluid collects in the abdomen.
as-needed dosing – Administering pain medication only when the animal shows recognizable signs of pain.
aspergillosis – A fungal infection caused by several species of Aspergillus fungi.
asphyxiation – A severe lack of oxygen resulting from inability to breathe.
aspiration – The use of a suction device to withdraw fluid from the body.
aspiration pneumonia – Inflammation caused by inhalation of food particles or fluids into the lungs.
asthma – A respiratory condition marked by recurring episodes of labored breathing, wheezing, and coughing, triggered by oversensitivity to environmental conditions.
astringent – A substance that causes tissues, such as mucous membranes, to shrink or dry out.
atherosclerosis – A hardening of an artery caused by deposits made of cholesterol, other fatty substances, or cellular debris that accumulates inside the artery.
atopy – Allergy characterized by itching and redness of the skin; may also include discharges from the eyes or nose.
atria – Plural form of the word atrium.
atrial fibrillation – Irregular contraction of the atria (upper heart chambers) caused by abnormal electrical activity in the heart.
atrial standstill – A failure of the electrical impulses in the upper chambers of the heart, which results in a lack of contraction of those chambers.
atrial thrombosis – A heart condition caused by a blood clot in the atrium of the heart.
atrioventricular valve – The valve between the upper (atrial) and lower (ventricular) chambers of the heart.
atrium – The upper chamber of the heart that receives blood from the veins and pushes it into the ventricle.
aural plaque – In horses, a white growth caused by a virus that develops in and around the ears.
autoimmune – An immune response that is developed against the animal’s own tissues.
autonomic nervous system – Specialized set of neurons controlling and regulating basic, unconscious bodily functions such as breathing and heart beat.
avian tuberculosis – A slowly spreading, chronic infection of birds caused by the bacteria Mycobacterium avium and characterized by gradual weight loss.
awn – A slender, bristle-like appendage found on the spikelets of many grasses.
axon – Extensions of neurons that transmit electrical charges away from the cell body.


B cell – A type of white blood cell that produces antibodies.
bacteremia – The presence of bacteria in the bloodstream.
bacteria – The plural form of the word bacterium.
bacterial disease – Disease caused by invading bacteria or an overgrowth of usually harmless bacteria.
bacterium – A microscopic, single-celled organism that may cause disease or may be a harmless, or even helpful, part of an animal’s normal internal or external environment.
barbering – Excessive chewing of hair or feathers that leads to bald patches of skin.
baroreceptors – Nerve endings in blood vessels that are sensitive to blood pressure changes.
basal cells – Cells at the base of the top layer of the skin.
basking – The behavior of a cold-blooded animal lying in the sun to increase its body temperature.
basophil – A type of white blood cell that releases histamine as part of the body’s allergic response.
benign – Something that is nonharmful or noncancerous.
besnoitiosis – Infectious disease caused by protozoa of the genus Besnoitia, transmitted by certain biting flies and ticks, found in Africa, France, and Mexico.
beta cells – Cells in the pancreas that produce insulin.
biceps brachii tendon – Tendon of the biceps brachii, a major muscle of the upper front leg that acts to bend the elbow joint.
biopsy – The removal of a small sample of tissue or fluid for examination. A sample is obtained in a way suited to the type of tissue and its location; it might be drawn out with a hollow needle and syringe, scraped with a curette, or cut away with a scalpel.
bladder – A stretchable, membranous sac-like structure in the body that holds fluids; the term is used most often to refer to the urinary bladder.
blastoma – A tumor composed of previously healthy young cells that never mature normally, but mutate into a cancer.
blastomycosis – A disease caused by Blastomyces fungi that can affect several species of animals or humans; infection may occur in the skin, lungs, or other body organs.
blepharitis – Inflammation of the eyelids.
blind spot – The small circular area, insensitive to light, where the optic nerve enters the eye. See also optic disk.
blister – A fluid-filled bump on the skin.
blood cell count – The number of red blood cells, white blood cells, and platelets in a sample of blood. Also called a complete blood count (CBC).
blood cells – Any of the cells contained in blood. See also erythrocyte, leukoctye, platelet.
blood clot – A mass of blood cells, protein, and platelets, also known as a thrombus, that forms whenever there is a break or tear in a blood vessel.
blood poisoning – A disorder, also known as septicemia, in which bacteria or their toxins circulate in the bloodstream.
blood pressure – The force exerted by the blood against the walls of the blood vessels, especially the arteries.
blood transfusion – A procedure in which another animal’s blood is introduced into the body to counteract blood loss, anemia, or other conditions.
blood typing – The identification of blood groups in order to match donor blood with the recipient’s blood for a blood transfusion.
bloodborne – Carried by or transmitted through blood.
bloodstream – The flow of blood through the circulatory system of an organism.
body cavity – An enclosed space in the body that contains organs, such as the cranial, spinal, thoracic, and abdominal cavities.
boid snakes – Snakes related to boa constrictors. The group includes pythons.
bone marrow – A soft tissue filling the spaces of the spongy tissue found at the ends of long bones. It produces red blood cells, most types of white blood cells, and platelets.
borreliosis – Disease caused by bacteria of the genus Borrelia. See Lyme disease.
botulism – Infection caused by ingesting food or dead flesh containing toxins produced by the bacterium Clostridium botulinum, or by absorbing toxins in the gastrointestinal tract. It results in rapid paralysis and death.
brachycephalic – Short-headed or broad-headed.
brachygnathia – Abnormal shortness or recession of the lower jaw.
brachytherapy – A cancer treatment that involves internal radiation therapy.
brackish – Water that is a mixture of fresh and salt water.
bradycardia – A slower than normal heart rate.
brain – The controlling center of the nervous system in vertebrates, connected to the spinal cord and enclosed in the cranium.
brain stem – One of the 3 main sections of the brain; it controls many basic life functions.
brain stem auditory evoked response (BAER) – Records electrical activity in the pathway from the sound receptors in the ear to the brain stem and cerebrum.
breed – A group of animals or organisms having common ancestors and certain distinguishable characteristics.
breeding – Sexual reproduction of animals, either spontaneously or planned and supervised by human beings.
broad-spectrum antibiotics – Antibiotics that are effective against a wide range of bacteria.
bronchial – Relating to the bronchi, the bronchial tubes, or the bronchioles, the body’s airways.
bronchitis – Inflammation of the bronchial airways.
bronchoscopy – Interior examination of the airways with an endoscope.
buck – The male of certain mammal species, such as rabbits, antelope, and deer.
budgerigar – A small Australian parrot commonly kept as a pet; also called a budgie or parakeet.
bumblefoot – A foot abscess in sheep, guinea pigs, or birds caused by a localized bacterial infection.
bursa – A fluid-filled body sac located between a tendon and a bone or at points of friction.


calcification – The abnormal hardening or stiffening of a body part caused by deposits of calcium.
calcinosis – The abnormal depositing of calcium salts contributing to hardening of a part or tissue of the body.
calcinosis cutis – A condition in which calcium deposits form in the skin; they can appear as small, thickened, “dots” on the abdomen.
calcitonin – Hormone secreted by the parathyroid glands that regulates levels of calcium in the bloodstream.
calcium deficiency – A lack of calcium in the body that can result from insufficient calcium or vitamin D in the diet and can cause bone deformities.
caloric – Relating to heat or calories.
cancer – A malignant tumor or growth that destroys healthy tissue.
cancer pain – Pain resulting from primary tumor growth, a spreading cancerous disease, or the toxic effects of chemotherapy or radiation.
candidiasis – A fungal disease caused by Candida albicans that affects the mucous membranes and the skin.
Canidae – Scientific name for dogs, foxes, and wolves.
canine – Relating to animals of the Canidae family, primarily dogs.
canine distemper (hardpad disease) – A highly contagious, usually fatal viral disease of dogs, ferrets, mink, raccoons, and other mammals.
canine herpesviral infection – A severe, often fatal, viral disease of puppies, sometimes referred to as fading or sudden-death syndrome. In adult dogs, it may be associated with upper respiratory infection or an inflammation of the vagina marked by pain and a pus-filled discharge (in females) or inflammation of the foreskin of the penis (in males).
canine thrombopathia – A hereditary disorder of blood platelets that causes bleeding from the nose and gums, and tiny purple or red bruises as a result of bleeding under the skin.
canine tooth – Long, pointed tooth used primarily for holding food in place in order to tear it.
cannibalism – The act of eating a member of an animal’s own species.
capillary – The smallest type of blood vessel, which connects small blood vessels that branch off from arteries and veins.
capsule – A medication consisting of an active ingredient and fillers, enclosed in a cylindrical coating usually made of gelatin; designed to be taken by mouth.
carcass – The dead body of an animal.
carcinogen – A cancer-causing substance or agent.
carcinoma – An invasive, malignant tumor derived from epithelial tissues (tissues that make up the skin, glands, mucous membranes, and organ linings).
cardiac – Of or relating to the heart.
cardiac output – The amount of blood pumped from the heart during a specified period of time.
cardiac shunts – Abnormal openings between chambers of the left and right sides of the heart.
cardiac tamponade – A buildup of fluid in the sac around the heart, which increases pressure on the heart and gradually interferes with its ability to pump blood.
cardiomyopathy – A disease in which the heart muscle is weakened.
cardiopulmonary resuscitation (CPR) – An emergency procedure, often employed after cardiac arrest, in which massage of the heart, artificial respiration, and drugs are used to maintain the circulation of oxygenated blood to the body. Also called cardiopulmonary-cerebral resuscitation (CPCR).
cardiovascular system – The body system that consists of the heart and the blood vessels (veins and arteries).
carnivore – A flesh-eating animal.
carpal – Relating to bones in the wrist; a wrist bone.
carpal joint – Any of the joints between the carpal bones.
carrier – An animal that, without becoming ill, harbors or spreads disease-causing microorganisms.
cartilage – A somewhat elastic connective tissue that is found at the ends of bones and helps reduce friction as joints move.
castration – Most often refers to surgical removal of the testicles; less commonly may refer to removal of the ovaries.
cataract – Condition in which the lens of the eye progressively loses transparency, which often results in loss of vision.
cathartic – A drug given to increase the passage of gastrointestinal contents, to cleanse the bowel before radiography or endoscopy, to eliminate toxins from the gastrointestinal tract, and to soften feces after intestinal or anal surgery.
catheter – A thin flexible tube that is inserted into a body cavity, duct, or vessel to allow passage of fluids.
cationic – A substance or class of detergents that are locally corrosive, causing skin, eye, and mucous membrane injury similar to that of alkaline corrosive agents.
ceiling effect – Situation in which an increased dose of a pain-relieving drug provides incrementally smaller gains in pain relief.
cell – The smallest functioning unit in the structure of an organism.
cell body – The center portion of a neuron.
cellular infiltrates – Gas, fluid, or dissolved matter that enters cells or tissue.
centesis – Procedure in which a needle is inserted into a structure (for example, the chest or urinary bladder) of an animal to remove fluid or air.
central nervous system – The part of the nervous system that includes the brain and spinal cord.
cercariae – Parasitic larvae of trematode worms.
cerebellar hypoplasia – Lack of development of the cerebellum, the section of the brain that controls motor function.
cerebellum – The cauliflower-shaped brain structure located just behind the cerebrum and above the brain stem.
cerebrospinal fluid – The fluid surrounding the brain and spinal cord.
cerebrum – One of 3 main sections of the brain; area where sensory and motor nerve activity is coordinated.
cesarean section – A surgical procedure in which the abdomen and uterus are cut open and the young are delivered through the abdomen.
cestode – Intestinal parasitic worm of the class Cestoda, with a flat, segmented body; tapeworms.
chelonians – Tortoises and turtles.
chemotherapy – The use of chemical agents to treat diseases, especially cancer.
cherry eye – Swelling and inflammation of the third eyelid, especially in dogs.
chlamydiosis – Infection with a bacteria of the genus Chlamydia.
Chlamydophila – Bacteria that cause serious respiratory infections in birds.
cholesteatomas – Cysts on the eardrum that may extend into the middle ear.
chondrosarcoma – A malignant tumor of cartilage.
chordae tendineae – Strands of connective tissue in the heart that connect the valves to the papillary muscles of the heart’s ventricles.
choroid – A membrane between the retina and sclera of the eye.
chromosome – Dense strands of material in the cell nucleus that carry the individual’s genetic material (DNA).
chronic – A condition that persists over a long period of time, often months or longer.
chronic pain – Pain that persists for longer than the expected time frame for healing, or pain associated with progressive, noncancerous disease, such as osteoarthritis.
cilia – Tiny, hairlike projections that line the outer part of cells in some tissues, including the lower respiratory tract.
cilia-associated respiratory Bacillus – Bacteria that can cause chronic respiratory disease in rats and mice; transmitted by direct contact.
ciliary muscles – The muscles in the eye that change the shape of the lens in order to keep vision in focus.
cleft palate – A congenital abnormality that creates a gap along the center of the roof of the mouth.
cloaca – In amphibians, fish, birds, and reptiles, an opening through which the digestive, urinary, and reproductive tracts exit the body.
cloacal prolapse – A condition in which the cloaca protrudes outside the body.
cloacitis – Inflammation of an animal’s cloaca. See cloaca.
clostridia – Bacteria that can cause severe intestinal disease or spread toxins through the bloodstream.
clot – A collection of red blood cells, white cells, and platelets, bound together by protein fibers, that plugs holes in blood vessels.
coagulation – The process by which liquid blood is transformed into a clot.
cobalt therapy – A type of radiation therapy that uses radioactive cobalt to treat cancer.
Coccidia – A group of protozoan parasites (small, single-celled organisms) that infect the intestinal tract of animals.
coccidioidomycosis – A dustborne, noncontagious infection caused by inhalation of fungal spores.
coccidiosis – A serious disease in cattle, sheep, goats, hogs, poultry, and rabbits, and less serious in dogs, cats, and horses. It is caused by protozoans (Coccidia) that invade and may destroy the lining of the intestines.
cochlea – A snail-shaped cavity in the inner ear, containing the organs of hearing.
coelomitis – Inflammation of the coelom, or abdomen, in retiles.
cognitive dysfunction – Senility; similar to Alzheimer’s disease in people.
cold-blooded – Animals that do not maintain a constant internal body temperature; instead, their temperature is greatly influenced by their environment.
colibacillosis – A form of diarrhea caused by Escherichia coli bacteria.
colic – Severe abdominal pain caused by spasm, obstruction, or distention of the intestines; there are many possible causes.
colitis – Inflammation of the colon.
collagen – A fibrous protein that forms tendons, ligaments, and connective tissue; also found in skin, bone, and cartilage.
colon – The large intestine.
colonoscopy – Examination of the inside surface of the colon using a tube inserted through the rectum.
colony – A group of organisms of one species that live and interact closely with each other in an organized fashion.
colostrum – The watery fluid rich in antibodies and nutrients that is produced by a mother after giving birth and before producing true milk.
colt – A young male horse.
colubrid – A snake of the Colubridae family, including adders, vipers, cobras, rattlesnakes, and coral snakes.
combination chemotherapy – Using a combination of drugs that target different sites or that employ different mechanisms to maximize destruction of cancer cells.
companion animal – Any animal kept by humans for companionship or pleasure rather than for utility; a pet.
compensatory mechanism – Any one of several specific responses the body uses in combating heart disease to maintain normal circulation.
complementary therapy – Therapy used in addition to conventional treatments.
compulsive behavior – Otherwise normal behaviors that occur out of context or so often that they interfere with normal activity.
computed tomography (CT) – A computer-enhanced x-ray procedure used to detect abnormalities in various body organs.
conduction – Passage of the electrical impulses that govern the pumping of the heart.
conformation – The structure or outline of an item or entity, determined by the arrangement of its parts.
congenital defect – An abnormality that is present at birth, as a result of either heredity or environmental influence such as a toxin or infection.
congestion – An abnormal buildup of fluid in an organ or area of the body.
congestive heart failure – A condition marked by weakness, shortness of breath, or an excessive buildup of fluid in the tissues or body cavities when the heart fails to maintain adequate blood circulation.
conjunctiva – The mucous membrane lining the inside of the eyelids.
conjunctivitis – Inflammation of the mucous membrane lining the inside of the eyelid. Also called pink eye.
constipation – Difficulty in passing bowel movements; incomplete or infrequent passing of hard stools.
constricted toe syndrome – A condition in newly hatched birds in which a tough ring of tissue forms around a toe joint, partially cutting off circulation.
contagious – Describes a condition that can spread from one organism to another.
contaminated – Unclean or polluted because of contact with harmful substances.
contraction – Pumping action of the heart muscle or other muscles.
contrast procedure – Specialized x-ray technique in which the animal is given a dye that shows up on the x-ray film to help provide more detailed images of body organs.
convulsion – See seizure.
coprophagia – Eating feces.
cornea – The transparent outer part of the eye that covers the iris and pupil and admits light into the eyeball.
coronavirus – A family of viruses that chiefly cause respiratory infections.
corticosteroid – Any of the steroid hormones made by the adrenal gland or their synthetic equivalents; commonly used to reduce inflammation.
cortisol – A steroid hormone produced by the adrenal gland that regulates carbohydrate metabolism and maintains blood pressure.
counterconditioning – A method for reducing unwanted behavior by teaching a pet to replace it with a more favorable behavior.
counterirritant – A substance that, when applied, irritates the skin and thereby reduces the inflammation of underlying tissue.
counterpressure – Pressure applied to reduce bleeding.
cranial – Relating to the skull, or cranium; toward the head end of the body.
cranium – The portion of the skull enclosing the brain.
cream – A semisolid mixture made for application to the skin or mucous membranes.
crop – In many birds, a pouch in the gullet where food is stored and sometimes partially digested before passing to the stomach.
cross matching – Blood typing test done to ensure that a blood donor and recipient have compatible blood types.
crotalids – Snakes of the genus Crotalidae, including pit vipers (rattlesnakes, for example).
cryptococcosis – A fungal disease that may affect the respiratory tract (especially the nasal cavity), central nervous system, eyes, and skin (particularly of the face and neck of cats).
cryptorchidism – A developmental defect marked by the failure of one or both testes to descend into the scrotum.
cryptosporidiosis – Intestinal infection with Cryptosporidium parasites, the primary sign of which is diarrhea.
Cryptosporidium – A genus of single-celled protozoal parasites that causes intestinal infection in several species, including humans.
CT scan – See computed tomography.
culture – A method of encouraging a microorganism to grow in a laboratory in order to identify specific bacteria or viruses that may be present.
Cushing’s disease – A hormonal disease characterized by overproduction of cortisol from the adrenal gland; most often caused by a tumor of the pituitary gland in the brain.
cutaneous – Of or relating to the skin.
cyst – A closed, fluid-filled growth in otherwise normal tissue.
cystitis – Inflammation of the bladder.
cystocentesis – Extraction of a sample of urine directly from the bladder using a needle and syringe.
cytokine – A protein secreted by cells of the immune system that helps regulate inflammatory responses.
cytology – The study of the structure and function of individual cells.
cytotoxic – Substance that is poisonous to cells.


debilitated – Having greatly decreased energy and strength.
debulking – A surgery done to remove part of a cancer or tumor.
decongestant – A medication that reduces mucosal congestion.
defecate – To expel feces from the intestinal tract.
defibrillation – A process of shocking the heart in a specific way to restore a coordinated heart beat and a pulse.
deficiency – A lack of something that is required for normal body function.
degeneration – A condition that causes a gradual deterioration in the structure or function of a body part.
degenerative joint disease – A form of arthritis characterized by gradual loss of cartilage of the joints. Also called osteoarthritis.
dehydration – A lack of sufficient water within the body.
dendrite – Extension of a neuron that receives signals from other neurons and transmits electrical charges to the cell body.
dental abscess – An infected cavity in a tooth, soft tissue surrounding the teeth, or bone of the jaw.
dental malocclusion – A misalignment of the teeth in which the upper and lower surfaces fail to come together properly.
depression – In animals, this usually refers to lowered activity and lack of interest in surroundings.
dermatitis – Inflammation of the skin.
dermatologist – A specialist in the treatment of skin disorders.
dermatophytosis – A fungal infection of the skin. Also known as ringworm.
dermis – The middle layer of the 3 layers of the skin.
descending aorta – The part of the aorta that passes through the chest and into the abdomen, supplying blood to the trunk and rear legs.
desensitization – A way to gradually teach a pet to tolerate a situation by carefully exposing it to that situation in small steps.
detergent – A cleansing substance, especially a liquid soap.
dewlap – Loose skin on the underside of an animal’s neck; this is normal in many species.
diabetes insipidus – A metabolic disorder caused by a lack of antidiuretic hormone, which leads to production of large amounts of dilute urine and excessive thirst.
diabetes mellitus – A metabolic disorder characterized by a deficiency in the hormone insulin and an accompanying inability to properly digest sugars; signs include excessive urination, too much sugar in the blood, thirst, hunger, and weight loss. See also insulin.
diagnosis – The identification of a disease based on its signs, physical examination, and appropriate tests.
diaphragm – A thin muscle that separates the abdominal and thoracic cavities and expands the chest during respiration.
diarrhea – The abnormally frequent discharge of soft or liquid feces.
diastole – The first half of a heartbeat, during which the upper chambers of the heart (atria) contract and send blood into the lower chambers (ventricles).
diestrus – A short period of sexual inactivity between 2 estrus periods, during which the uterus is prepared for a fertilized egg.
dietary indiscretion – Unhealthy eating, as of trash, large amounts of table scraps, or other inappropriate food.
digestion – The process by which an animal processes food and absorbs nutrients.
digestive tract – The system of organs responsible for digestion.
dilate – To widen or enlarge.
dilated cardiomyopathy – A heart disease in which the heart is enlarged and the heart muscle is weakened.
direct life cycle – A pattern in which a parasite needs only 1 host in which to grow, breed, and reproduce itself.
discharge – Any fluid that emerges from a sore or infection.
disinfectant – A chemical used to kill germs.
dislocation – Displacement of a body part, especially of a bone, from its usual fitting in a joint.
displacement activity – The resolution of a behavior conflict by performing a seemingly unrelated activity such as grooming or sleeping.
disseminated intravascular coagulation – A condition in which small blood clots develop throughout the bloodstream, blocking small blood vessels and destroying the platelets and clotting factors needed to control bleeding.
dissemination – The spread of a disease-causing organism throughout the body, causing signs in multiple parts of the body.
distemper – An airborne viral disease of dogs and some related animals such as raccoons; signs include fever, vomiting, diarrhea, loss of appetite, dehydration, tremors, weakness, and incoordination.
distended – Swollen or expanded, as by pressure from within; dilated.
distillation – The evaporation and subsequent collection of a liquid by condensation as a means of purification.
diuretic – A medicine usually prescribed to reduce fluid overload; increases urine production.
DNA – Deoxyribonucleic acid; the molecule that encodes genetic information in the nucleus of cells and is capable of self-replication.
doe – A female of any of several species, including rabbits and deer.
dormant – Existing in a temporarily inactive form or state, or biological rest.
duodenum – The first and smallest portion of the small intestine, beginning at the stomach.
dustborne – Carried by exterior or interior dusts, often used to describe bacteria transmitted in this way.
dysecdysis – Improper or incomplete shedding of the skin in reptiles.
dysplasia – Abnormal growth, development, or placement of body parts.
dystocia – Abnormal or difficult birth.
dystrophy – A degenerative condition caused by a nutritional defect or disorder.


ear canal – The tube connecting the external ear with the eardrum.
ear mites – Tiny organisms resembling ticks that can infect the ear canal of animals, especially dogs and cats.
eardrum – The membrane at the end of the ear canal that transmits sound waves to the middle ear.
ecdysis – The act of molting, or shedding, an outer skin layer.
echocardiography – A type of ultrasonography used to examine the heart.
eclampsia – A condition marked by a sudden drop in blood calcium levels, caused by the production of milk after giving birth; often leads to convulsions and coma.
ecosystem – A community of interdependent living organisms and the environment they inhabit.
ectoparasite – A parasite that lives on its host’s skin, hair, or feathers, such as fleas and ticks.
ectotherm – An animal that cannot regulate its own body temperature and is instead dependent on the temperature of its surroundings (for example, reptiles and amphibians); commonly referred to as cold‑blooded.
ectropion – A slack eyelid edge that is turned outward.
edema – The abnormal accumulation of fluid in a tissue.
egg binding – A condition in birds and reptiles in which the female is unable to lay a developed or partially developed egg.
ehrlichiosis – A tickborne bacterial infection that affects white blood cells.
elapid – A member of a family of venomous snakes with hollow fangs, such as cobras.
electrocardiogram (EKG) – A recording of the heart’s electrical activity made by attaching a set of electrodes to the skin.
electrocardiography – Recording of the electrical activity of the heart.
electrolytes – Ions, or salts, such as sodium and potassium, that are present in blood and other bodily fluids and help regulate various metabolic processes.
electromyography – An electrical recording of muscle activity that aids in the diagnosis of diseases affecting muscles and peripheral nerves.
ELISA – An abbreviation for enzyme-linked immunosorbent assay, a test used to detect a disease-causing agent such as a virus.
Elokomin fluke fever – An infectious disease of dogs acquired by eating raw fish infected with flukes that carry the disease-causing bacteria.
emaciation – A condition in which the animal is abnormally thin, generally as the result of malnutrition or disease.
embolism – Obstruction of a blood vessel by a blood clot that breaks off from its point of origin and lodges elsewhere.
embolus – Portion of a blood clot that breaks free and travels through the cardiovascular system.
embryo – The earliest stage of development of an animal in the womb, before any of the major body organs have formed.
emphysema – Abnormal accumulation of air in tissues; often affects the lungs and causes breathing difficulties.
emulsifier – A chemical agent used to bind together substances that normally do not bind.
emulsion – A suspension of one liquid in another with which the first will not mix (for example, oil and water).
encephalitis – Inflammation of the brain; often caused by an infection.
encephalitozoonosis – A protozoal infection of rabbits and occasionally of mice, guinea pigs, rats, and dogs that affects multiple organs; also called nosematosis.
encysted – Enclosed in a cyst, sac, bladder, or vesicle (for example, an encysted tumor).
endocarditis – Inflammation of the membranes lining the heart cavity.
endocrine – Related to glands that deliver hormones into the bloodstream.
endoparasite – A parasite that lives inside its host, such as a heartworm.
endoscope – An instrument for examining visually the interior of a bodily canal or a hollow organ such as the colon, bladder, or stomach.
endoscopic gastric biopsy – A sample of stomach tissue taken with an endoscope, a long, flexible tube equipped with a camera and other instruments that is inserted through the mouth into the stomach.
endoscopy – A procedure in which a tube called an endoscope is inserted into a hollow organ. The tube generally has a camera for maneuvering and frequently has tools such as forceps or scissors attached.
endotoxin – A substance found in the cell walls of some bacteria that causes toxic shock, fever, and inflammation in mammals.
endotracheal tube – Tube inserted into the trachea to deliver oxygen or anesthetic gas.
engorge – To fill with blood.
enterolith – A hard mass composed of magnesium ammonium phosphate crystals that forms around a foreign object (such as a stone or nail) in the large intestine, most commonly in horses.
enterotoxemia – The presence of bacterial toxins in the bloodstream.
entropion – A turned-in edge of the eyelid, which leads to irritation of the eyeball from the eyelashes.
enzootic – A disease that is continually present in a particular location.
enzyme – A protein that speeds up a biological process such as digestion.
eosinopenia – A decrease in the number of eosinophils (a type of white blood cell) in the bloodstream.
eosinophil – A type of white blood cell that plays a role in the immune response by ingesting bacteria and other foreign cells, immobilizing and killing parasites, and participating in allergic reactions.
eosinophilia – An increase in the number of eosinophils (a type of white blood cell) in the bloodstream.
epidemic – An outbreak of a contagious disease that spreads rapidly and widely.
epidermis – The outer layer of the 3 layers of the skin.
epidural anesthesia – Injection of pain-relieving or numbing drugs into the space surrounding the spinal cord to decrease sensation in parts of the body below that portion of the spinal cord; often used to provide anesthesia for surgery.
epilepsy – An inherited disease that causes seizures; generally requires treatment with anticonvulsants.
epithelial – Having to do with the skin (epithelium).
epizootic lymphangitis – A fungal disease that affects the skin, lymph vessels, and lymph nodes of the limbs and neck of horses.
equine – Related to or having to do with horses.
equine granulocytic ehrlichiosis – An infectious disease of horses caused by a bacterium found in the bloodstream and transmitted by ticks.
equine infectious anemia – An incurable, viral bloodborne infection of horses transmitted by blood-sucking insects.
equine morbillivirus pneumonia – A short-term, often fatal, viral respiratory infection of horses caused by the Hendra virus.
equine protozoal myeloencephalitis – Protozoal infection of the nervous system of horses.
equine sarcoid – See sarcoid.
equine viral arteritis – A short-term, contagious, viral disease of the horse family that affects multiple body systems.
erosion – A shallow or superficial ulcer or sore, typically on the skin.
erythrocyte – A red blood cell.
erythropoiesis – The formation and production of red blood cells.
erythropoietin – A hormone secreted by the kidneys that triggers the production of red blood cells in bone marrow.
esophagus – The muscular tube that connects the throat to the stomach.
estrous – Of, relating to, or being in heat (estrus).
estrous cycle – The recurring physiological and behavioral changes that take place from one period of estrus (heat) to another.
estrus – A recurring period of increased sexual desire during which a female mammal will allow sexual activity and is capable of conceiving.
euthanasia – The deliberate, painless killing of an incurably ill or injured animal; also called putting to sleep or putting down.
excretion – The process for removing waste matter from the blood, tissues, or organs.
exertional rhabdomyolysis – A metabolic disorder caused by intense exercise in which toxins from muscle injury can damage other tissues, especially the kidneys.
exoskeleton – A skeletal structure outside the body, as in insects.
exotic pets – Nontraditional pets; animals that are not domesticated.
expectorant – A medicine that thins airway secretions, making them easier for the animal to cough up.
exposure – Contact with or proximity to some environmental condition, toxin, or infectious agent.
eyelid atresia – A congenital condition in which the eye opening is reduced or closed entirely over otherwise normal eyes.


failing heart – Any heart with a reduced ability to contract.
farcy – A contagious, incurable bacterial infection of horses that may affect the skin or lungs. Also called glanders.
farrier – A person who makes and fits horseshoes.
fasting – Withholding food from an animal for a certain length of time.
fatal – Causing or capable of causing death.
fatty acid – One of the major components of fat, used by the body to supply energy and build tissues.
fecal – Relating to or consisting of feces.
feces – The solid waste from an animal.
feed hopper – A simple device that uses gravity to keep a trough or bowl filled with food as animals eat.
feline – Of or having to do with cats.
feline distemper – See feline panleukopenia.
feline infectious enteritis – See feline panleukopenia.
feline infectious peritonitis – A progressive viral infection of cats that affects multiple body systems and causes a variety of signs.
feline leukemia virus – A cancer-causing virus of cats that infects cells of the immune system and frequently results in death.
feline lymphoma – A tumor of the immune system that is the most frequently diagnosed cancer of cats.
feline panleukopenia – A viral infection of cats that affects multiple body systems; most infections cause no signs, but if signs are present the infection is serious and usually fatal.
femur – The large bone of the upper hind limb; also known as the thigh bone.
fertility – The ability to produce offspring.
fertilization – The combination of a sperm cell and an egg cell into a developing organism.
fetal – Having to do with a fetus or its development.
fetal membranes – The thin layers of tissue that surround the embryo during its development. Also called amniotic sac.
fetus – A developing animal from the stage at which the major organs form until birth. See also embryo.
fever – Abnormally high body temperature.
fibrocartilage – A type of strong, relatively inelastic connective tissue.
fibroma – A benign tumor formed in fibrous or connective tissue.
fibromatosis – A thickening and invasive growth in tendon sheaths.
fibropapillomatosis – A condition characterized by the presence of abnormal growths of tissue (fibrous papillomas) in both the epidermal and dermal skin layers.
fibrosarcoma – A malignant tumor that arises from cells that produce connective tissue, predominantly found in the area around bones or in soft tissue.
fibrosis – The formation of excessive, dense, tough connective tissue.
fibrous osteodystrophy – Generalized loss of mineral salts throughout the skeleton due to an increased rate of bone destruction resulting from hyperparathyroidism (excess parathyroid hormone secretion). Also known as osteitis fibrosa cystica.
fibrous tissue – Tissue consisting primarily of high-strength fibers, such as ligaments and tendons.
filly – A young female horse.
filtration – The process of removing waste and particulate matter from water.
first aid – Emergency medical treatment given until more thorough, professional veterinary treatment can be obtained.
fistulous withers – A condition in which connective tissue in a horse’s withers region becomes infected and inflamed.
flagellate – A single-celled organism with one or more flagella, whip-like appendages used for locomotion.
flashing – Scratching (as pertains to fish).
flea – A small, wingless insect that lives on the skin of mammals or birds and feeds on their blood.
flexor tendons – Any of several tendons that act to bend a joint.
flora – Bacteria that normally live in a part of the body, such as the intestines.
fluke – Any of almost 6,000 species of parasitic flatworms.
fluorescein staining – A test that uses orange dye (fluorescein) and a specialized light to detect foreign bodies or scratches in the eye.
fly strike – A condition in which flies lay their eggs on wounds, dead skin, or skin covered with feces. The maggots that hatch can destroy large areas of skin. Also called cutaneous myiasis.
foal – The offspring of a horse or other equid, up to the age of 1 year.
forceps – A surgical instrument used to grasp and hold tissue.
forebrain – The front segment of the brain that includes the cerebrum, thalamus, and hypothalamus.
foreskin – The loose fold of skin that covers the glans of the penis. Also called prepuce.
fossorial species – An animal that is specially adapted for digging.
fracture – The partial or complete break of a bone.
frostbite – Tissue damage caused by freezing temperatures, which can result in tissue death if exposure is extensive.
fry – Newly hatched fish.
fungal – Caused by, or related to, a fungus.
fungus – A classification of living things that are immobile but cannot gain energy from sunlight, as plants can; some cause infections in animals and people.
fur mite – External parasites that live on the skin and fur and cause itching.
fur slip – A condition in chinchillas in which patches of fur are lost due to rough handling or fighting.


gait – The manner of walking or moving.
gastrin – A hormone that prompts the release of gastric acid in the stomach, usually secreted by the stomach and small intestine.
gastrinoma – A tumor of the pancreatic islet cells.
gastroenteritis – Inflammation of the stomach and intestine, often resulting in diarrhea, vomiting, and cramps.
gastrointestinal – Having to do with the stomach and intestines.
gastrointestinal system – The internal organs responsible for digestion, including the stomach and the intestines.
gastrostomy – Insertion of a tube directly into the stomach for the purpose of providing nutrition.
genetic – Having to do with genes or heredity.
genitalia – External sex organs.
geotrichosis – A rare fungal infection caused by Geotrichum candidum, a fungus found in soil, decaying organic matter, and contaminated food.
gestation – The period of development of an animal inside its mother’s womb.
Giardia – A water-dwelling, single-celled microorganism that causes diarrhea in many species, including humans.
giardiasis – A gastrointestinal disorder caused by infection with Giardia microorganisms, characterized by diarrhea, stomach cramps, nausea, and vomiting.
gingivitis – Inflammation of the gums.
glanders – A contagious, incurable, slowly progressive bacterial infection of horses that may affect the skin or lungs. Also called farcy.
glaucoma – An eye disorder marked by increased pressure within the eye, which can damage the interior of the eye and lead to blindness.
gliding membrane – A flap of skin which allows an animal to glide but not fly, as is found in sugar gliders and flying squirrels. Also called a patagium.
globin – A globular protein that combines with heme to form hemoglobin. See hemoglobin.
glomerulonephritis – Inflammation of the glomeruli of the kidney.
glomerulonephrosis – A common disease of older rats involving inflammation of the blood vessels in the kidney.
glomerulus – Structure in the kidney made up of special blood vessels that help filter blood; each kidney contains thousands of these.
glossitis – Inflammation of the tongue.
glucagon – A hormone that helps convert stored carbohydrates into glucose (sugar) so they can be used as energy.
glucocorticoid – A type of corticosteroid (see corticosteroid) that is involved with metabolism of carbohydrates, protein, and fat. They are frequently used in medicine for their anti-inflammatory and immuno-suppressive properties.
glucose – A simple sugar that is one of the body’s main sources of energy.
glucosuria – The presence of glucose, a sugar, in the urine.
gnat – A small, 2-winged biting fly.
goiter – An enlarged thyroid, often caused by iodine deficiency.
goitrogen – A goiter-producing substance.
gonads – The sex organs that produce reproductive cells (sperm and eggs). In the male, these are the testes; in the female, the ovaries.
gout – A painful inflammation of joints, often in the foot, that is most often caused by a buildup of uric acid and salts.
granule – A small grain or particle; or a compound of powder particles that have been formed into larger pieces.
granulocyte – A specialized type of white blood cell, produced in the bone marrow, that plays a role in immune responses to invading microorganisms.
gray patch disease – A herpesviral infection of the skin that affects turtles, characterized by sores that spread across the turtle’s body.
growth plate – Zone of cartilage near the ends of long bones where new bone is formed.
gut loading – The process of feeding prey animals highly nutritious food in order to pass the nutrients on to animals that eat them.
guttural pouch – Areas of the eustachian tubes that form a bag or pouch, located under the base of the skull in horses.


habituation – A simple form of learning that involves the ending of, or decrease in, a reaction to a situation as a result of repeated or prolonged exposure to that situation.
halogenated – Combined or treated with a halogen (fluorine, chlorine, bromine, iodine).
hardpad disease – See canine distemper.
head tilt – A condition in which the head is kept tipped to one side; can be caused by many different diseases, including inner ear infection and neurological problems.
heart disease – Any structural or functional abnormality of the heart that impairs its normal functioning.
heart failure – Any heart abnormality that results in failure of the heart to pump enough blood to meet the body’s needs.
heat – See estrus.
heat exhaustion – A condition caused by overexertion in high temperatures or overexposure to the sun.
heat stroke – A collapse brought on by prolonged periods of heat stress or heat exhaustion. Signs include cessation of sweating or panting, extremely high body temperature, and unconsciousness.
helminth – A general term for a group of parasitic worms.
hemangiosarcoma – A rare, rapidly growing, highly invasive cancer that originates from cells that line blood vessels (endothelial cells).
hematology – The study of blood, its chemistry and components.
hematoma – A mass of blood, generally clotted, that forms in an organ or body cavity due to a ruptured blood vessel.
hematopoiesis – The formation and development of the various blood cells.
heme – A complex molecule containing iron that combines with globin to form hemoglobin.
hemoglobin – The iron-rich compound in blood that carries oxygen throughout the body.
hemolysis – A condition in which red blood cells are ruptured.
hemorrhage – Bleeding; escape of blood from a broken blood vessel.
hemostasis – A process that stops blood flow, particularly clot formation.
hemostatic – A compound that inhibits bleeding.
hepatic – Related to or affecting the liver.
hepatic encephalopathy – A syndrome that occurs as a result of liver disease; signs include circling, head pressing, aimless wandering, weakness, poor coordination, blindness, excessive drooling, aggression, dementia, seizures, and coma.
hepatitis – Inflammation of the liver.
hepatopathy – General scientific term for liver disease.
herbicide – One of a group of chemicals used to destroy weeds.
herbivores – Animals, such as rabbits or horses, that eat only plants.
hereditary – Transmitted genetically from parent to offspring.
hernia – The protrusion of a body part through the lining that normally encloses it.
herpesvirus – Any of a group of viruses that cause disease in humans and animals. Herpesviruses often cause sores or rashes and generally remain in the body even when not causing signs.
hibernation – A state of inactivity and unconsciousness, generally during the winter months.
histiocytoma – A soft tissue giant cell tumor.
histology – The anatomical study of the microscopic structure of tissue.
histoplasmosis – A noncontagious infection caused by a soil fungus, occurring when airborne spores are inhaled.
hives – The least severe type of anaphylactic (allergic) reaction. Small bumps occur on the skin. The hair may stand up over these swellings and sometimes they itch.
hock – The ankle joint of rabbits, horses, and other 4-legged animals that walk on the same bones that form the toes in humans.
hormone – A compound produced by a gland in the body that stimulates other parts of the body and controls their activity.
host – A living animal or plant on or in which a parasite lives. See parasite.
hot packing – A supportive treatment that involves application of moist heat to reduce inflammation.
human-animal bond – The emotional relationship existing between humans and companion animals.
husbandry – The care provided to maintain domestic animals.
hutch – A pen or coop for a small animal, such as a rabbit.
hutch burn – A disease caused by wet and dirty hutch floors in which the area surrounding the anus and genital region becomes inflamed and chapped, and then infected with disease-causing bacteria.
hydration – The process of providing an adequate amount of fluids to body tissues.
hydrocephalus – A condition in which excess fluid accumulates within the skull because of a blockage in the normal channels that allow it to flow out of the skull.
hygiene – Actions taken to maintain cleanliness and health.
hygroma – A cyst or sac filled with fluid.
hyper- – Prefix meaning over, above, too much, too high, excessive.
hyperadrenocorticism – A disease caused by production of too much cortisol. Also called Cushing’s disease.
hypercalcemia – Abnormally high levels of calcium in the blood, characterized by weakness, nausea, confusion, and lethargy.
hyperextension – Extension of a joint beyond its normal range of motion.
hyperlipemia – Excessive levels of fat in the blood.
hyperparathyroidism – An excess of parathyroid hormone in the blood.
hyperplasia – An abnormal increase in the number of cells in an organ or tissue with consequent enlargement.
hypertension – An increase in the body’s blood pressure.
hyperthermia – Abnormally high body temperature.
hyperthyroidism – A disorder caused by an excess of the thyroid hormones.
hypertrichosis – A common endocrine disorder resulting from chronic excess of the hormone cortisol (Cushing’s disease). Signs include development of an abnormally long or heavy hair coat, excessive thirst and urination, increased appetite and weight, an enlarged abdomen, and bulging eyes.
hypertrophy – Enlargement of an organ or tissue.
hyperuricemia – Abnormally high levels of uric acid in the blood, caused by excessive production or insufficient excretion of the compound.
hypo- – Prefix meaning below, less than normal, deficient, too little, too low.
hypoadrenocorticism – A deficiency of adrenal gland hormones. Also called Addison’s disease.
hypocalcemia – Abnormally low levels of calcium in the blood.
hypoglycemia – Abnormally low levels of glucose in the blood, often caused by a deficiency of insulin, characterized by trembling, weakness, hunger, confusion, unconsciousness, and in severe cases, death.
hypoparathyroidism – Disorder characterized by low calcium levels, high phosphate levels, and either temporary or permanent insufficiency of parathyroid hormone.
hypoplasia – A condition of abnormal development in which a body part remains small, immature, or underdeveloped.
hypoproteinemia – Abnormally low levels of protein in the blood.
hypothalamus – The part of the brain below the thalamus that functions to regulate bodily temperature and certain metabolic processes.
hypothermia – Abnormally low body temperature.
hypothyroidism – A deficiency of thyroid hormone, which can cause weight gain, constipation, and cold sensitivity.
hypoxia – Condition in which the level of oxygen in the blood is too low; anoxia.


idiopathic – Used to describe a disorder or disease that has no apparent cause.
immersion – A method of administering medication to or treating fish by placing them in a tank containing the medication.
immune – Resistant to infection or disease.
immune response – The body’s reaction to an infectious agent or other foreign “invader.” This includes recognition of the invader and development of a protective defense.
immune system – The system within an animal that recognizes an infectious agent or other foreign “invader” and mounts an immune response. The immune system includes various organs, such as the thymus gland, spleen, and lymph nodes, as well as specialized cells found throughout the body.
immune-mediated – Describes a process initiated or controlled by the immune system.
immunization – The process of making an individual immune to a given disease, generally through vaccination.
immunized – Rendered resistant to toxins or infectious agents, especially by injection or vaccination.
immunodeficiency – An inability of the immune system to produce a normal immune response.
immunoglobulin – Protein antibodies produced by the body to fight a disease.
immunomodulator – A drug that helps regulate the immune system’s activity.
immunostimulant – A drug or agent that increases an immune response.
immunosuppressed – A state in which the immune system is inhibited by medications during the treatment of other disorders, or by stress or infection.
immunosuppression – Interference with the normal function of the immune system.
immunotherapy – Any of several treatments of disease that involve inducing, enhancing, or suppressing an immune response.
impedance – Obstruction of normal flow or passage, such as an obstruction of blood flow.
implant – A drug, such as a long-lasting tablet, inserted under the skin.
incisor – Front teeth that are used to grasp or cut food.
inclusion body disease – Any disease characterized by inclusion bodies, small foreign bodies within cells.
incontinence – The inability to control urination or defecation.
incubation period – The time after an infection has been contracted but before any signs are apparent.
infection – A disorder that occurs when microorganisms invade the body and multiply. Infectious microorganisms include bacteria, viruses, fungi, and parasites.
infectious – A condition that is passed from animal to animal by a virus, bacterium, or other agent.
infectious canine hepatitis – A contagious viral disease of dogs with signs that vary from a slight fever and congestion of the mucous membranes to severe depression, severe reduction in white blood cells, and deficiency of blood clotting.
infertility – The inability to produce offspring.
infest – To live as a parasite in or on.
infestation – The act of infesting or state of being infested.
infiltrate – Material deposited within the space between cells in a tissue.
inflammation – A localized protective response to injury or other tissue damage. The response includes increased blood flow in the surrounding capillaries (causing redness), swelling, increased temperature in the area, and pain.
inflammatory – Characterized or caused by inflammation.
influenza – A respiratory infection caused by an influenza (flu) virus.
ingest – To take food or liquid into the body by swallowing or absorption; eat.
inhalation – The act of breathing in.
inherited – Passed genetically from parents to offspring.
inhibitor – A substance that restrains or retards physiological, chemical, or enzyme action.
initiation – The first step in the transformation of healthy cells into cancerous cells.
inoculation – Introduction of a substance into the tissues or fluids of the body; this is often done for the purpose of preventing or curing certain diseases.
inorganic – Composed of minerals rather than living material; without carbon.
insect growth regulator – A class of drugs that helps control pests such as fleas by disrupting their development and maturation.
insecticidal – Of or related to a chemical substance used to kill insects.
insulin – A hormone secreted by the pancreas that is essential for digestion, especially that of carbohydrates. See also diabetes mellitus.
insulinoma – A common pancreatic islet tumor that affects the insulin-secreting beta cells.
interdigital furunculosis – Abscesses on the webbing between the toes.
interferon – Protein produced by immune cells that helps fight viral infection. See also cytokines.
intermediate host – An animal in which juvenile parasites reside before passing to the final host animal to develop into adults and breed.
intestinal protozoan – Any of a number of single-celled microorganisms that infect or dwell within the intestines. Many cause disease, but others are harmless or even beneficial.
intestine – The part of the digestive tract between the stomach and the anus, divided into the small intestine and the large intestine.
intoxication – Another term for poisoning or toxicosis.
intramuscular – Directly in or into the muscle.
intraocular – Having to do with, entering, or residing within the interior of the eye.
intravascular – Inside the blood vessels.
intravenous – A method of administering fluids or medications directly into a vein. Also known by the abbreviation IV.
intubation – Insertion of a breathing tube into the trachea.
intussusception – The doubling up of a section of intestine on itself in accordion-like folds, causing obstruction.
invasive – A tumor that tends to spread locally into adjacent tissues.
invertebrate – An animal without a backbone, such as an insect or spider.
involuntary – Spontaneous or automatic; not controllable by the conscious mind.
iodine deficiency – Insufficient iodine in the diet that can lead to goiter.
iodine toxicity – Harmful effects, which may include goiter, of an excess of iodine in the diet.
iris – The muscular diaphragm in the eye that controls the size of (and therefore the amount of light passing through) the pupil.
irradiation – Bombardment with radiation, generally as a treatment for tumors.
islet cell tumor – A cancer of the islet cells of the pancreas.
islet of Langerhans – Cluster of 3 kinds of endocrine cells scattered throughout the pancreas that secrete several hormones, including insulin.
isolation – The process of keeping diseased or potentially diseased animals separate from other susceptible animals.


jaundice – A condition characterized by yellowing of the skin, eyes, and mucous membranes caused by an excess of bile products in the blood.
joint – The site where 2 or more bones meet. Joints may be movable or immovable.
joint mice – Fragments of cartilage in joints.
jugular – Of, relating to, or located in the region of the neck or throat.


keratin – The hard protein that makes up hair, fingernails, claws, horns, scales, and the shafts of feathers.
keratinization – Creation of new skin cells near the base of the epidermis that migrate upwards, producing a compact layer of dead cells on the skin surface.
keratoacanthoma – A benign skin tumor of dogs that includes a cyst filled with keratin.
ketosis – A condition resulting from excess buildup of ketones, a waste product, in the blood.
kidney – Either of a pair of abdominal organs that filter waste from the blood and help maintain proper water and salt balance.
kidney failure – Loss of normal function of the kidneys, which can be either a short- or longterm condition.
kit – The young of any of a number of mammals, such as foxes and rabbits.


laceration – A cut or tear in the skin.
lacrimal gland – The gland near the eye that produces tears.
lactation – The production of milk by a female mammal.
Lactobacillus species – A group of bacteria that create lactic acid and play a normal, often beneficial, role in many animals’ bodies.
lagenidiosis – A fungal infection of dogs that affects the skin and blood vessels.
lagophthalmos – An inability to completely close the eyelids due to malformation.
lameness – An inability to walk or move normally, often, but not always, caused by pain in the limb.
larva – An immature form or life stage of an insect or parasite.
larvae – Plural form of the word larva.
larval – Of or pertaining to larvae.
larynx – The part of the throat often called the “voice box” in humans.
latent – In an inactive or hidden stage.
laxative – A drug used to promote bowel movements.
leg banding – The process of putting coded bands onto the legs of captive birds, generally while they are young, for purposes of identification.
Legg-Calvé-Perthes disease – Deterioration of the top of the femur (the femoral head) seen in young miniature and small breeds of dogs, characterized by a lack of blood supply and destruction of blood vessels of the bone.
lens – The transparent, oval-shaped part of the eye that focuses light on the retina.
leptospirosis – An infection characterized by fever and jaundice caused by bacteria of the genus Leptospira.
lesion – Any abnormal change in the structure or function of a part of the body.
lethargy – Lack of energy; apathy.
leukemia – A cancer of the blood and bone marrow, characterized by increased numbers of white blood cells.
leukocyte – Blood cell type involved in immune responses; commonly called white blood cells.
leukocytic – Having to do with leukocytes.
leukocytosis – An increase in the number of white blood cells in the bloodstream.
leukogram – A diagnostic blood test that counts the number of different white blood cells circulating in the bloodstream.
leukopenia – A decrease in the number of white blood cells in the bloodstream.
libido – Sexual drive; desire to mate.
lice – A group of small, wingless insects that live on the skin of birds and mammals and suck their blood.
life cycle – A description of all the stages in the life of an organism.
ligament – A band of tough, fibrous tissue connecting bones or cartilage at a joint, or supporting an organ.
liposarcoma – A benign tumor of fatty tissue.
listeriosis – An infection by the bacteria Listeria monocytogenes which can affect the nervous system, or lead to abortion or blood poisoning.
liver – A large abdominal organ with many functions, such as filtering and removing toxins from the blood, storing glycogen, and producing and secreting bile.
localized – Restricted or limited to a specific body part or region.
lockjaw – A spasm of the jaw muscles that keeps them tightly closed, most frequently caused by tetanus. See also tetanus.
long bones – Any of several elongated bones of the legs (for example, the femur and humerus) that have a roughly cylindrical shaft.
lordosis – An abnormal inward curving of the spine in the lower area of the back.
lumpectomy – Surgical excision of a tumor with minimal removal of surrounding tissue.
lumpy jaw – The most common and least severe form of actinomycosis, a bacterial infection that causes hard masses to form in the mouth and jaw.
lung – Either of 2 spongy, saclike respiratory organs that occupy the chest cavity and provide the blood with oxygen while removing carbon dioxide during respiration.
luxation – Dislocation.
Lyme disease – Tickborne infection of animals and humans caused by Borrelia burgdorferi bacteria that can cause rash and arthritis. Also known as Lyme borreliosis.
lymph node – Small organ of the immune system that contains cells that fight infections, neutralize toxins, and produce antibodies.
lymph – A clear, watery fluid derived from body tissues that collects through the lymphatic system and is then returned to the bloodstream.
lymphadenitis – Inflammation of the lymph nodes.
lymphangitis – Inflammation of lymphatic vessels.
lymphatic system – The network of small vessels that collects the fluid surrounding the cells and returns it to the bloodstream.
lymphocyte – White blood cells that produce antibodies, neutralize toxins, and fight infections and cancer.
lymphocytic choriomeningitis – A viral infection of mice characterized by fever, vomiting, neck stiffness, and slow pulse.
lymphocytosis – An increase in the number of lymphocytes in the bloodstream.
lymphoid – Of or relating to the lymph or lymphatic tissue.
lymphoma – A cancer of certain white blood cells that begins in a lymph node or other lymphoid tissue.
lymphopenia – A decrease in the number of lymphocytes in the bloodstream.


macrophage – A type of white blood cell, larger than most, that consumes infectious agents and other foreign cells and destroys them.
maggot – The legless, soft-bodied, wormlike larva of any of various flies, often found in decaying matter.
magnetic resonance imaging (MRI) – An advanced, noninvasive diagnostic imaging technique that uses powerful magnets to examine tissues and organs.
malabsorption – Faulty or abnormal absorption of nutrients from the digestive tract.
malaise – A feeling of illness or depression.
maldigestion – Abnormal breakdown and absorption of foods from the digestive tract.
malignant – Cancerous; a tumor that invades other nearby tissues or spreads throughout the body.
malnourished – Affected by an improper or insufficient diet; undernourished.
malocclusion – See dental malocclusion.
mammals – Animals that produce milk to feed their young and have 4 limbs and at least some hair.
mammary – Of or relating to the mammary glands of a female mammal.
mammary glands – The organs that produce milk.
mange – Any of several skin disorders caused by an infestation of mange mites.
marking – Depositing urine or feces to send a social signal, such as claiming territory.
marsupials – Mammals, chiefly but not exclusively from Australia, that carry their young in an external pouch.
masking behavior – Behavior to hide injury or weakness, especially by prey animals.
mass – Another word for a tumor or growth.
mast cell – A cell that secretes histamine found in connective tissue.
mastitis – Inflammation of the mammary glands, often caused by bacterial infection.
maternal immunity – The resistance to disease provided by antibodies passed through the mother’s first milk (colostrum) to newborn mammals, usually lasting for several weeks.
mechanism – A process by which something is accomplished.
megakaryocyte – A large cell found in bone marrow that produces platelets.
melanoma – A type of skin tumor, often malignant, that contains dark pigment.
melioidosis – An uncommon bacterial infection, usually of rodents, that can be passed to humans.
membrane – A thin layer of tissue that lines an organ or body cavity.
meninges – Thin layers of tissue that line the brain and spinal cord.
meningitis – Inflammation of the meninges.
meningoencephalitis – Inflammation of the brain and of the membrane lining the brain and spinal cord.
metabolic activity – The chemical processes occurring within a living cell or organism that are essential to maintenance of life.
metabolic bone disease – Any of several diseases of the bones caused by an imbalance of calcium and other minerals in response to abnormal metabolism.
metabolic disorder – Any disorder in which normal body processes are disturbed, leading to an increase or decrease in the end products of those processes.
metabolic rate – Metabolism over time; the speed at which metabolism occurs.
metabolism – The physical and chemical processes that take place in the body to maintain life.
metacarpal bones – Bones in a vertebrate animal’s forefoot similar to the bones in the human hand between the wrist and the fingers.
metastasis – The spread of a malignant tumor to distant parts of the body.
metastatic calcification – Abnormal, hardened deposits of calcium in soft tissues.
metastatic tumor – A tumor formed from cells that have traveled from the original tumor to another site in the body.
metatarsal bones – Bones in a vertebrate animal’s hind foot similar to bones in the human foot between the toes and the ankle.
metritis – Inflammation of the uterus.
microbiology – The study of small organisms such as bacteria, viruses, fungi, and other single-celled life forms.
microchipping – A method of identifying pets that involves the insertion of a small glass-encased electronic chip under the skin.
microfilaria – Immature life stage of heartworms that is found in the bloodstream.
microhabitat – The small, specialized environment in which an organism lives.
microorganism – A bacterium, virus, or other organism that is too small to see without a microscope.
midges – Gnatlike flies that are often found near water; some species bite and feed on blood.
miliary dermatitis – Skin irritation with small, solid, bumps typically spread over the back, neck, and face.
mineralocorticoids – Hormones produced by the adrenal cortex that help control the body’s balance of sodium and potassium salts.
mineral – A solid crystalline substance arising from inorganic processes. Many minerals are nutrients that are needed for normal body functions.
mite – Any of a number of very small arachnids, related to spiders and scorpions, many of which live as parasites on various species of animals.
mitral valve – The valve between the left chambers of the heart, through which the blood flows from the atrium to the ventricle.
molar – A large grinding tooth in the back of the mouth.
mold – Any of various fungi that often cause disintegration of organic matter.
molt – In birds, the normal loss of feathers in preparation for the growth of new feathers. In reptiles, the normal shedding of skin; also called ecdysis.
Mongolian desert mice – Another term for gerbils, related to their origin.
monkeypox – A viral disease, similar to but milder than smallpox, originally detected in monkeys.
monocyte – A type of white blood cell that plays a role in immune defense by moving from the bloodstream into the tissues, enlarging, and becoming a macrophage. See also macrophage.
monocytopenia – A decrease in the number of monocytes in the bloodstream.
monocytosis – An increase in the number of monocytes in the bloodstream.
mortality – The rate of death in a population.
mosquito – A winged insect that feeds on blood and can transmit disease.
motor – Relating to motion, or body movement.
motor function – The ability to produce body movement by complex interaction of the brain, nerves, and muscles.
motor neurons – Nerve cells that carry signals from the brain that control muscle activity.
MRI – See magnetic resonance imaging.
mucosa – See mucous membrane.
mucous membrane – The layer of cells that lines the tubular organs of the body, such as the digestive and respiratory tracts.
mucus – A slippery secretion produced by glands of the mucous membranes.
multifocal – Relating to or arising from many locations.
murmur – A vibration heard coming from the heart or major blood vessels.
muscle – A tissue composed of fibers capable of contracting (and thus producing motion).
muscular wasting – The steady loss of muscle mass and strength.
musculoskeletal – Having to do with the muscles, bones, and joints.
Mustelidae – Latin term for the scientific family that includes ferrets, mink, and skunks.
mutation – A spontaneous, permanent change in genetic material that is passed to the organism’s offspring.
muzzle – An animal’s nose and jaws.
mycetoma – Infection of the skin and underlying tissues that has the appearance of a nodule or tumor.
mycobacterial infections – See mycobacteriosis.
mycobacteriosis – Infection by mycobacteria, a group that includes the bacteria responsible for leprosy and tuberculosis.
mycoplasma – The smallest known type of bacteria, which lack cell walls.
mycosis – Fungal infection.
mycotoxicosis – Disease caused by toxins produced by fungi.
myelography – A specialized x-ray procedure in which a dye is injected into the cerebrospinal canal to outline the spinal cord.
myiasis – Maggot infestation. Also known as strike.
myocardial disease – A disorder of the heart muscle.
myocarditis – A local or widespread inflammation of the heart muscle with degeneration or death of the heart muscle cells.
myocardium – The muscular tissue of the heart.
myopathy – General term referring to any skeletal muscle disease.
myositides – Diseases that produce a mainly inflammatory reaction in muscle.
myositis – Inflammation of a muscle, characterized by pain, tenderness, and sometimes spasm in the affected area.
myxomatosis – A severe viral disease in rabbits, characterized by the formation of myxoma, or soft, gelatinous tumors, and subsequent swelling around the head, face, and genitals.


nagana – An often fatal disease of vertebrates transmitted by the bite of the tsetse fly; may affect multiple body systems and often causes anemia.
nares – The openings of the nose.
nasal – Having to do with the nose, often its interior.
nasal cavity – The air-filled space above and behind the nose, on either side of the septum.
nasal discharge – Material, typically mucus, emerging from the nose.
nasogastric tube – A feeding tube that is inserted through the nose into the stomach.
nasolacrimal duct – A duct that moves tears from the eye to the nose.
nebulization – Conversion of a substance, such as a medication, from a liquid or solid state into a fine mist or vapor.
necropsy – An animal autopsy.
necrotic dermatitis – Inflammation of the skin characterized by localized death of tissue.
necrotic meningoencephalitis – A disease caused by infection of the brain with microorganisms, with signs that may include depression, lethargy, labored breathing, loss of appetite, bluish skin, and a pus-like discharge from the nose.
nematode – A parasitic worm; also called a roundworm.
neonatal – Having to do with newborn offspring.
neoplasia – The formation of a tumor.
neoplasm – A tumor.
neosporosis – An infectious disease of dogs and other animals caused by the protozoan parasite Neospora caninum.
nephritis – Inflammation of the kidney.
nephrotic – Of or relating to the kidneys.
nephrotic syndrome – Signs of disease in the kidney that may include protein in the urine, low levels of protein in the blood, a buildup of fluid in the abdomen, shortness of breath, and swelling in the legs.
nerve – Specialized tissues that transmit electrical impulses serving to relay sensory or motor information between the nervous system and body organs.
nest box – A man-made box provided for animals to nest in.
neuroendocrine tissue tumors – Tumors that can develop from neuroendocrine cells (found in tissues that have both nervous system and hormone-producing functions) in the adrenal or thyroid glands.
neurologic – Of or pertaining to the nervous system.
neurologic signs – Impairments of perception or behavior caused by damage to the central nervous system.
neuromuscular – Having to do with the terminations of nerves in muscle tissue.
neuron – The specialized cells of the nervous system responsible for transmitting electrical signals.
neuropathic pain – Pain resulting from damage to a nerve or some other part of the central nervous system.
neurotransmitter – A chemical released by a nerve cell that passes signals to other nerve cells, or to muscles or glands.
neuter – To remove the internal reproductive organs (that is, the ovaries and uterus or testes) of an animal in order to prevent reproduction.
neutropenia – A decrease in the number of neutrophils in the bloodstream.
neutrophil – A common type of white blood cell that engulfs and destroys bacteria and other foreign cells.
neutrophilia – An increase in the number of neutrophils in the bloodstream.
nevus – A congenital pigmented area on the skin; sometimes called a birthmark.
Newcastle disease – A contagious viral disease in birds, whose signs include coughing, sneezing, diarrhea, tremors, and twitching.
nictitating membrane – A thin membrane in many animals that can extend across the eye to protect it; also called the third eyelid.
nit – The small egg of a louse, typically found glued to hair.
nitrates – Chemical compounds that can be used by plants and algae as food, or removed by water filtration.
nocardiosis – A chronic, noncontagious disease caused by Nocardia bacteria found in soil, decaying vegetation, and other environmental sources.
nocturnal – An animal that is active only or primarily at night.
nodule – A small, irregular, rounded mass.
noncontagious – Not contagious; not communicable by contact.
nonregenerative anemia – A decrease in the number of red blood cells, which the bone marrow is not able to fully compensate for by creating new red blood cells.
nonsteroidal anti-inflammatory drug (NSAID) – A group of medications other than corticosteroids that relieve pain, fever, and inflammation.
nonviremic – Animals that, despite being infected by a virus, show no evidence of it in the bloodstream.
nuclear scintigraphy – A diagnostic procedure involving dosing the animal with a radioactive element. This element is then detected within the body by means of a special camera attached to a computer, which generates the image.
nutrient – A substance that nourishes a living thing.
nutrition – A source of nourishment; food.
nutritional deficiency – A lack in the type or amount of nutrients an organism receives.
nutritional osteodystrophy – Defective bone formation, as in rickets, caused by an imbalance of calcium and phosphorus in the diet.
nymph – The larval form of certain insects.
nymphomania – Prolonged estrus or sexually receptive behavior in a female animal.
nystagmus – Abnormal, involuntary, usually rapid movement of the eyeballs as a result of dizziness, head injury, or disease.


obstruction – Blockage of a passage in the body, as of the intestines.
ocular – Of or relating to the eye.
ocular fundus – The back layer of the eye opposite the pupil where light is detected by specialized nerve cells.
ointment – A healing salve intended for external application.
oncologist – A cancer specialist.
oncology – The field of medicine dedicated to the study, diagnosis, and treatment of cancer.
oocyst – A fertilized egg in the process of development; a zygote.
oomycosis – Infection with Oomycetes fungi, most common among fish.
opaque – Something through which light cannot pass.
ophthalmoscope – An instrument for viewing the interior of the eye.
opiate – A class of narcotic drugs derived from opium that can reduce pain, induce sleep, and suppress coughing.
opioid – Any of a class of synthetic drugs that are not derived from opium but have similar properties. See opiate.
opportunistic agent – An infectious substance or microorganism, not normally dangerous, that can cause disease when the body’s immune system is impaired or weakened.
opportunistic infection – An infection by a microorganism that normally does not cause disease but becomes capable of doing so when the body’s immune system is impaired or weakened.
optic disk – The point on the retina where the optic nerve enters the eye. Also called the blind spot.
optic nerve – The nerve that connects the eye to the brain and transmits visual information; also called the second cranial nerve.
optimal temperature zone – The preferred temperature range for a species.
oral – Having to do with the mouth.
oral cavity – The interior of the mouth.
orbit – The part of the skull that encloses and protects the eye and related structures.
organ – A structure composed of various types of tissues that has a specific function; most organs function as part of an organ system.
organic – Relating to a substance derived from a living organism; containing carbon.
organism – An individual form of life, such as a plant, an animal, a bacterium, or a fungus.
osmoregulation – Maintenance of an optimal balance in the concentration of salts in the body’s fluids.
osteoarthritis – See degenerative joint disease.
osteochondritis dissecans – A condition usually seen in young animals in which the immature joint cartilage separates from the underlying bone.
osteochondrosis – A condition in which immature joint cartilage separates from the bone and floats loosely in the joint cavity, where it can cause inflammation and interfere with proper bone formation.
osteomalacia – A condition in adult animals in which the bones soften because of an imbalance in calcium and phosphorus metabolism.
osteomyelitis – Inflammation of the bones caused by a bacterial infection.
osteoporosis – A condition marked by loss of bone mass due to poor nutrition, age, or nursing.
osteosarcoma – A malignant bone tumor.
otitis – Inflammation of the ear.
otitis externa – Inflammation of the external ear canal.
otitis interna – Inflammation of the inner ear.
otitis media – Inflammation of the middle ear.
otoscope – An instrument with a light and a magnifying lens to aid visual examination of the ear canal.
outbreak – A sudden occurrence or appearance, as of a disease.
ovary – The female reproductive organ that produces eggs, as well as the hormones estrogen and progesterone.
ovariohysterectomy – The surgical removal of the ovaries and uterus.
over-the-counter – Sold directly to the public without a doctor’s prescription.
ovulation – The release of an egg (ovum) from the ovary for possible fertilization.
oxygenate – To treat, combine, or infuse with oxygen.
oxytocin – A hormone that stimulates milk flow, causes the uterus to contract during and after birth, and increases maternal behavior.


paecilomycosis – An infection caused by fungi of the genus Paecilomyces that affects the lungs and other organs.
palliative – A drug or medicine used to relieve or soothe the signs of disease.
palpation – Examination by finger pressure to detect growths, changes in underlying organs, and unusual tissue reactions to pressure.
pancreas – A large gland that secretes digestive enzymes and hormones, such as insulin, that regulate blood sugar levels.
panhypopituitarism – A disorder in which the pituitary gland and nearby tissues, including the hypothalamus, are compressed or damaged, leading to a lack of several different hormones.
papilloma – A wart or other benign growth on the skin or other vascular tissues.
papillomatosis – Any condition marked by the presence of many papillomas. See papilloma.
papule – A small, hard, round bump or protuberance on the skin.
paralysis – Partial or total loss of motor function or sensation in part of the body.
paramyxovirus – Any of a group of viruses including those that cause measles, mumps, rubella, and Newcastle disease.
paranasal – Adjacent to the nasal cavity.
parasite – Any living organism that lives inside, with, or close to another living creature (called a host) and uses the host as a source of food, shelter, or other requirements.
parasitic – Of, related to, or caused by a parasite.
parasitism – A close relationship in which one species, the parasite, benefits at the expense of the other, the host.
parathyroid glands – Glands that secrete parathyroid hormone and calcitonin.
parathyroid hormone – A hormone that acts with vitamin D and another hormone, calcitonin, to regulate the levels of calcium in the body.
parvovirus – A family of viruses including a type that causes a highly contagious intestinal disease of dogs.
passerine – Describes the group of perching birds and songbirds such as jays, blackbirds, finches, warblers, and sparrows.
paste – A semisolid drug dosage form for treating animals.
pasteurellosis – Infection with Pasteurella bacteria, which most frequently infect the respiratory tract.
patagium – See gliding membrane.
patella – Kneecap; a flat triangular bone located at the front of the knee joint.
patellar luxation – Displacement of the kneecap.
patent ductus arteriosus – A heart defect in which the ductus arteriosus (the temporary fetal blood vessel connecting the aorta and the pulmonary artery) does not close at birth.
pathogenic – Producing disease, or having the capability to cause disease.
pathologic – Relating to or caused by disease.
pathologist – A veterinarian or physician who specializes in examining tissue samples to identify the cause of disease or death.
pectoral muscle – Any of the muscles that connect to the chest at one end and to the bones of the front limbs at the other end.
pelvic canal – The passage from the abdomen through the bones of the pelvis to the outside of the body.
penicillosis – Infection by mold of the genus Penicillium, which usually affects the nose and sinuses.
penis – The external male organ of copulation, used to transfer semen to the female and to expel urine.
pentastomes – Worms that infest the respiratory system of birds, reptiles, and mammals. Also called tongue worms due to their appearance.
perianal – Situated or occurring around the anus.
pericardial disease – Disease of the pericardium, the sac surrounding the heart.
pericardiocentesis – Insertion of a needle through the pericardium (the sac surrounding the heart) to withdraw fluid.
pericarditis – Inflammation of the sac or lining around the heart.
pericardium – The sac-like membrane surrounding the heart.
periodontal – Of or relating to the gums.
perioperative – The period immediately before and after a surgical procedure.
peripheral nervous system – The parts of the nervous system outside of the brain and spinal cord.
peritoneal cavity – The space between the membranes lining the abdominal cavity and the abdominal organs.
peritoneal lavage – Rinsing of the peritoneal cavity with saline or other fluids as a part of a diagnostic test to look for signs of infection or inflammation.
peritoneum – The membrane lining the abdominal cavity and the organs found within it.
peritonitis – Inflammation of the peritoneum, often caused by infection or injury to the gastrointestinal tract.
permeability – The rate at which a liquid or gas passes through a membrane or other porous material.
persistent – Tenaciously or obstinately continuing, often for a long time.
pesticide – A chemical that kill pests, especially insects.
pH – A measure of the acidity or alkalinity of a fluid or damp substance.
phaeohyphomycosis – A fungal infection that usually occurs because of contamination of tissue at the site of an injury.
phagocyte – A cell that ingests and kills other substances, especially microorganisms.
phagocytosis – The process by which cells engulf and digest microorganisms and cellular debris; an important defense against infection.
phalanx – Any of the bones that form the digits, corresponding to fingers and toes in humans.
pharmacology – The science that deals with the chemistry, development, uses, and metabolism of drugs.
pharynx – The throat.
pheochromocytoma – A tumor of the adrenal gland that is able to secrete adrenaline (epinephrine) and other hormones.
pheromone – A chemical secreted by an animal that influences the behavior or development of others of the same species; often serving to attract the opposite sex.
phobia – An intense and excessive fear of something.
photoperiod – The amount of time per day that an organism is exposed to sunlight or artificial light.
photoreceptor – Any structure that senses the presence of light.
photosensitization – A condition in which skin is overly sensitive to sunlight; distinct from sunburn.
pica – The eating of non-food items, such as gravel or dirt.
pigmentation – The deposition of coloring matter (pigment) in a cell or tissue.
pink eye – See conjunctivitis.
pinna – The large visible portion of the external ear.
pinworm – Any of a group of small, parasitic nematodes that live in the intestines of vertebrates.
piping – Refers to the activity of fish swimming near the surface of the water trying to gulp air.
pituitary – Related to the pituitary gland of the brain that produces hormones critical for control of many bodily functions.
pituitary dwarfism – Disorder of the pituitary gland in which a shortage of growth hormone leads to smaller than normal size.
pituitary gland – A small, oval, endocrine gland attached to the base of the brain which secretes hormones that control many other endocrine glands.
placenta – The organ that connects the fetus to the mother in most mammals and regulates the exchange of nutrients between them.
placental – Of or relating to the placenta.
plague – An acute and sometimes fatal bacterial disease, transmitted primarily by the fleas of rats and other rodents.
plasma – The clear, yellowish fluid portion of blood or lymph in which cells are suspended.
plasmodial organisms – Single-celled protozoal parasites that live within the bloodstream and cause malaria.
platelet – A type of small blood cell responsible for clotting. Also called a thrombocyte.
pleura – The membranes lining the outside of the lungs and the chest cavity.
pleural cavity – The space between the membranes lining the chest wall and the lungs.
pleurisy – Inflammation of the lining around the lungs (the pleura), causing pain, cough, chest tenderness, and shortness of breath.
pneumonia – Inflammation of the lung tissue, often accompanied by inflammation of the trachea and other large airways; also known as pneumonitis.
pneumonitis – See pneumonia.
pneumothorax – Air in the space between the lungs and the chest wall.
pododermatitis – Inflammation of the skin near the foot or hoof.
poison – A substance that causes illness, injury, or death if ingested.
polioencephalomalacia – A neurologic disease that leads to softening and degeneration in the outer layer of the brain.
poll evil – Bacterial infection and inflammation of a sac surrounding a tendon near the base of the skull in horses.
polyarteritis nodosa – Inflammation of the walls of arteries that affects multiple organs.
polycythemia – An increase in the number of red blood cells circulating in the bloodstream.
polydactyly – The presence of extra toes, which is a common inherited condition in cats.
polyp – A growth or mass projecting from the tissue of a membrane, sometimes tumorous.
polyphagia – Excessive appetite or overeating.
polysaccharide – A complex carbohydrate such as starch or cellulose, made up of sugar molecules in a chain structure.
porphyrin – A protein molecule that is one of the building blocks of hemoglobin, the molecule that carries oxygen in the bloodstream.
portosystemic shunt – A congenital defect in the blood vessels of the liver that reduces the ability of the liver to process waste products.
positive inotrope – Any of a class of drugs used to help the heart muscle contract.
postpartum hypocalcemia – See puerperal hypocalcemia.
powder – A formulation in which a drug powder is mixed with other powdered fillers to produce a final product.
predation – The hunting and eating of other animals.
predilection – A particular liking or preference.
predisposing factor – A condition or situation that increases the susceptibility to a particular disease or injury.
pregnancy toxemia – An often-fatal metabolic condition of pregnant guinea pigs, cows, and sheep, more common in those that are overweight, in which a buildup of toxins occurs in the bloodstream.
prenatal – Of or relating to the period before birth.
prepuce – A retractable fold of skin covering the penis in many mammals.
prevalent – Widely or commonly occurring.
priapism – An abnormal, persistent erection of the penis, often caused by spinal cord injury or injury to the penis.
primary factor – The main cause, or one of the main causes, of a disease or injury.
prognathia – Abnormal protrusion of the jaw, commonly the lower jaw.
prognosis – The prospect of survival or recovery following a disease or injury.
progressive – Tending to become more severe or wider in scope.
prokinetic – A drug that increases the movement of food through the gastrointestinal tract.
prolapse – The displacement of a body part from its usual position.
proliferative enteropathy – A disease of the intestinal tract in young pigs characterized by severe diarrhea and anemia; possibly caused by bacteria.
promoter – An agent that facilitates the development of cancer in cells.
promotion – The second step in the development of cancer.
prophylaxis – Administering antibiotics as a preventive measure to keep an infection from developing.
prostate gland – An organ of the male reproductive system that creates part of the fluid portion of semen.
prostration – Total exhaustion or weakness; collapse.
protein – Complex molecules made of amino acids that include many substances (such as enzymes, hormones, and antibodies) necessary for the proper functioning of an organism.
protocol – A method or regimen of treatment.
protozoa – Plural of protozoan.
protozoal – Of, related to, or caused by protozoa.
protozoan – Any of a large group of single-celled, usually microscopic organisms, that may be parasites.
protrusion – Something that sticks out.
pruritus – Severe itching; usually signalled by scratching.
pseudomyiasis – False strike (maggot infestation); the presence of fly maggots in the gastrointestinal tract (from ingestion) but without tissue infestation.
psittacine – Of or belonging to the family Psittacidae, which includes parrots, macaws, and parakeets.
psychotropic drug – Any of a group of drugs that are used to modify an animal’s behavior, including antidepressants, anti-anxiety drugs, and sedatives.
puberty – The phase during which an animal becomes sexually mature.
puerperal hypocalcemia – A life-threatening decrease in calcium usually seen in dogs 2 to 3 weeks after giving birth, caused by the loss of calcium from producing milk.
puerperal tetany – See puerperal hypocalcemia.
pulmonary – Of, relating to, or affecting the lungs.
pulmonary artery – The artery that carries venous blood from the right ventricle of the heart to the lungs.
pulmonary edema – Fluid in the lungs.
pulmonary hypertension – High blood pressure in the blood vessels of the lungs.
pulmonary valve – The valve that releases blood out of the right ventricle of the heart into the pulmonary artery.
pulse – The rhythmic throbbing of arteries produced by the regular contractions of the heart.
pupa – The nonfeeding, transformative stage between the larva and adult in insects.
pupil – The black circle in the center of the iris in the eye; the hole through which light enters the eye.
pus – A thick, yellowish-white fluid seen in wounds and sores and containing white blood cells, microorganisms, and tissue debris.
pustules – Small, inflamed, elevations of the skin filled with pus.
pyloric stenosis – A muscular constriction between the stomach and intestines.
pyoderma – Any skin disorder that includes formation of pustules or pimples.
pyometra – A disorder characterized by the accumulation of a large amount of pus in the uterus.
pythiosis – A disease caused by Pythium insidiosum, an organism similar to a fungus, which can affect the skin or gastrointestinal tract in dogs or cause skin disorders in horses or cats.


Q fever – A bacterial infection that mainly affects the respiratory or reproductive tracts of ruminants such as cattle and sheep, although other domestic animals, including dogs and cats may be infected. Also known as query fever.
quadriceps – Large muscle at the front of the thigh that acts to extend the knee.
qualitative – Of or related to a categorical observation of an object, for example breed or sex.
quantitative – Of or related to a numerical observation of an object, such as 5 pounds or 3 meters.
quarantine – To keep an animal separate from other animals to avoid spreading a disease or infection.
queen – A mature female cat, especially one kept for breeding purposes.


rabbit calicivirus disease – A highly infectious, contagious, and mostly fatal disease of domestic rabbits that affects the digestive system and causes internal bleeding. Also called viral hemorrhagic disease.
rabbitpox – An often fatal, generalized, viral disease of rabbits that causes pox marks on the skin as well as discharges from the nose and eyes.
rabbitry – A place where rabbits are kept or bred.
radiation – High-intensity energy waves emitted by radioactive elements, for example, x-rays.
radiation therapy – The use of radiation or radioactive substances to treat disease.
radiography – An imaging technique that produces an image on film or other sensitive surface by radiation, such as x-rays passing through an object.
radioisotope irradiation – A type of radiation therapy. See radiation therapy.
radiotherapy – See radiation therapy.
radius – The shorter and thicker bone in the lower forelimb of animals.
radon – A colorless, radioactive gaseous element used in radiotherapy.
range (as in range plants) – Extensive open land area where livestock wander and graze.
rash – A temporary outbreak on the skin’s surface that is often reddish and itchy.
receptor – A sensory nerve ending that responds to one of several stimuli, such as touch, temperature, light, taste, or pain.
recurrence – A repeated occurrence; reappearance or repetition.
recurrent – Happening again and again.
reflex – An unconscious, automatic movement that occurs in response to sensory stimulation, for example the extension of the knee when the tendon below the knee is tapped.
regenerative anemia – A form of anemia in which the bone marrow responds to the decreased number of red blood cells by increasing red blood cell production.
regurgitate – To flow in the opposite direction than normal, as in backward flow of blood within the heart; to bring undigested food up from the esophagus (rather than the stomach) to the mouth.
reinfestation – A reoccurrence of an infestation, as by fleas.
reinforcement – Reward; any event that increases the chances that a certain behavior will be repeated.
relapse – The return of an illness, especially after a period of apparent health or improvement.
remission – A decrease in or a temporary disappearance of the signs of disease.
renal – Of, relating to, or in the region of the kidneys.
replicate – Reproduce.
reproduction – The process that gives rise to offspring.
reproductive system – The organs involved in reproduction.
reptile – Any of a class of air-breathing, usually ectothermic (cold-blooded), vertebrate animals, generally covered in scales or plates; examples include lizards, snakes, and turtles.
resistance – An organism’s ability to keep from being affected by an infection; ability of a microorganism to withstand the effects of a previously effective drug or dosage.
resistant – Having the capacity to withstand; relating to or conferring immunity.
resorption – The process of reclaiming an established organ or structure in order to use its nutrients.
respiratory – Of, relating to, used in, or affecting respiration (breathing).
respiratory failure – Inadequate gas exchange or airflow in the respiratory system.
respiratory sinus arrhythmia – The small variations in heart rate in healthy, quiet animals that are caused by pressure changes in the chest associated with breathing.
respiratory system – The organs responsible for breathing, including the lungs, trachea, mouth, nose, and throat.
respiratory tract – The passages through which air enters and leaves the body.
reticulocyte – An immature red blood cell.
retina – The rear inner surface of the eye, responsible for picking up light and transmitting it to the brain as visual signals via the optic nerve.
retrovirus – Any of a family of viruses that store their genetic material as single-stranded RNA rather than 2-stranded DNA.
reverse osmosis – Purification process by which water is forced through an extremely fine membrane and a carbon filter to remove even more compounds than are removed during normal filtration.
rhabdomyolysis (sporadic exertional) – Severe cramping and stiffness of muscles following heavy exercise, leading to disintegration of muscle fibers; also called tying up.
rhinitis – Inflammation of the nose.
rhinosporidiosis – A chronic, nonfatal, fungal infection, primarily of the lining of the nasal passages and, occasionally, of the skin.
rickets – A nutritional disorder of young animals caused by a lack of phosphorus or vitamin D, leading to malformation of bones and lameness.
rickettsiae – A group of small bacteria that can live only within cells and that cause several diseases, including Rocky Mountain spotted fever, in animals and people.
ringtail – A ring-like constriction of the tail, affecting mice, rats, or hamsters, caused by low humidity and high temperatures, and eventually causing gangrene and loss or partial loss of the tail.
ringworm – A fungal skin infection affecting many animals and humans; dermatophytosis.
RNA – Ribonucleic acid; a nucleic acid found in all living cells essential for the manufacture of proteins and carrying genetic information.
Rocky Mountain spotted fever – An infection of humans, dogs, and other animals that is caused by Rickettsia rickettsii bacteria, transmitted by ticks.
rodenticide – A compound used to poison rodents.
root canal – The central cavity of a tooth that extends down into the roots of the tooth.
Rotavirus – A genus of viruses that cause intestinal infection in young animals of several species, including birds and pigs.
roughage – Another term for fiber, which aids digestion.
roundworm – See nematode.
ruminant – Any of various hoofed, even-toed, mammals such as cattle, sheep, goats, and deer, characteristically having a 4‑compartment stomach and chewing a cud consisting of partially digested food.


saline – A solution of salt (sodium chloride) and purified water that has the same concentration of salts as the bloodstream.
saliva – The clear liquid containing digestive enzymes and immune cells that is secreted into the mouth by the salivary glands.
salmon poisoning disease – An infectious disease in which the infective agent is transmitted through the various life cycle stages of a flatworm known as a fluke. See Elokomin fluke fever.
salmonellosis – Infection with Salmonella bacteria, most often characterized by gastrointestinal signs such as diarrhea.
sanitation – Measures and actions to maintain health through good hygiene.
sarcocystosis – Disease in which the muscles and other soft tissues are invaded by intermediate life stages of single-celled organisms of the genus Sarcocystis.
sarcoid (equine) – Fibrous tumor masses that resemble large warts. They commonly occur on the lower legs of horses.
sarcoma – A malignant tumor formed in connective tissue, bone, cartilage, or certain types of muscle.
scabies – Infestation by mites of the genus -Sarcoptes, which affect dogs, cats, horses, pigs, and other species; sarcoptic mange.
scar tissue – The pale, inflexible connective tissue that forms at the site of an injury.
scintigraphy – See nuclear scintigraphy.
sclera – The white outer coating that covers the eyeball, except for the central round area covered by the transparent cornea.
scoliosis – A congenital sideways curvature or deformation of the spine.
scraping – Cellular material obtained for examination by scratching a specific tissue with a clinical instrument.
screwworm – The larval stage of certain disease-spreading flies.
scrotum – The external pouch of skin and muscle containing the testes in male mammals.
scurvy – A nutritional disorder caused by a lack of vitamin C and characterized by bleeding of the skin and mucous membranes, tooth loss, weakness, and spongy gums.
scute – An external bony or horny plate or scale covering the skin of some reptiles, such as the shell of a turtle.
sebaceous gland – A skin gland that secretes the oil known as sebum into the hair follicles and onto the skin.
seborrhea – A disease of the sebaceous glands characterized by excessive secretion of sebum or an alteration in its quality, resulting in an oily coating, crusts, or scales on the skin.
sebum – Oily secretion from the sebaceous gland that helps lubricate the skin.
secondary hyperparathyroidism – The excessive secretion of parathyroid hormone by the parathyroid glands in response to hypocalcemia (low blood calcium levels).
secretion – The process of secreting (generating) a substance from cells, or bodily fluids such as saliva, mucus, or tears.
sedate – To administer sedatives, bringing about a relaxed state.
sedative – A drug or other agent that induces sedation, a state of calm, restfulness, or drowsiness.
sedentary – An adjective used to describe an animal or human that exercises little.
seizure – Any of several types of interruption in normal bodily control or thought processes, often characterized by uncontrollable stiffness or jerking of the body, face, or limbs.
semen – The viscous, whitish fluid containing sperm and seminal fluid that a male ejaculates during breeding.
semiaquatic – An animal that frequents water but does not completely live in it.
semilunar valves – Valves between the heart and the aorta, and between the heart and the pulmonary artery.
sensory – Of or relating to sensations of pain, position, touch, temperature, taste, hearing, vision, and smell.
sepsis – Illness resulting from the persistent presence of microorganisms or their toxins in the bloodstream. Also called septicemia or blood poisoning.
septal defect – A hole in the membrane, or muscle wall, dividing the chambers of the heart.
septic shock – A life-threatening condition caused by an infection in the bloodstream in which blood pressure falls dangerously low and many organs malfunction because of inadequate blood flow. See sepsis.
septicemia – See sepsis.
septicemic cutaneous ulcerative disease (SCUD) – A bacterial disease in turtles in which the scales are pitted.
serotype – A group of related microorganisms that are neutralized by the same antibodies.
service animal – Companion animal that is trained to help a person with disabilities, aid law enforcement personnel, help search for lost people, or other tasks.
sheath – An enveloping tubular structure, such as the tissue that encloses a muscle or nerve fiber.
shock – A condition of sudden failure of the circulatory system, brought on by excessive blood loss, severe infection, or nervous system dysfunction, among other causes.
sign – Indication or evidence of disease, for example weakness, coughing, or diarrhea.
silage – Animal feed made by storing green plant material, as in a silo.
sinoatrial node – The heart’s natural pacemaker, which generates rhythmic impulses that cause contractions of the muscle fibers of the heart.
sinus (cardiology) – A dilated channel or receptacle containing chiefly venous blood.
sinus (respiratory system) – Any of several bony cavities in the head connected to the nasal cavity.
sinus arrest – A pause or cessation of cardiac sinus pacemaker activity.
sinusitis – Inflammation of the lining of the sinuses in the head.
skeletal disorder – Disease affecting the development or structure of the bones.
skin appendage – A small or secondary attachment to the skin, such as hair follicles, oil and sweat glands, and claws.
skin tenting – Condition that occurs when a small section of skin is pinched away from the body does not snap back to its original position. It can be used to indicate the degree of dehydration of an animal.
small intestine – The long, narrow part of the digestive tract that lies between the stomach and the colon.
smear – A medical screening or diagnostic procedure in which a sample of cells (blood, for example) is collected and spread on a microscope slide for examination.
soft tissue – Any of the body tissues other than bone and cartilage.
solution – A drug dosage form that is dissolved in liquid, usually water.
solvent – A substance in which other substances are dissolved to create a solution.
somatostatin – A hormone produced chiefly by the hypothalamus that inhibits the secretion of growth hormone and various other hormones.
soundness – Freedom from injury, disease, or illness; without damage.
spasm – A sudden, involuntary contraction of a muscle or group of muscles.
spawning – The process by which some animals, such as certain fish, reproduce.
spay – To remove the internal reproductive organs (ovaries, uterus) of a female animal in order to prevent reproduction.
species – A subdivision of a basic biological group, the genus, containing individuals that resemble one another and that may interbreed.
spina bifida – A congenital defect in which the spinal column is imperfectly closed.
spinal – Of, relating to, or situated near the spine or spinal cord.
spinal cord – The long bundle of nerve tissue that runs from the brain to the end of the spinal column and connects to the majority of the peripheral nerves.
spine – The backbone of a vertebrate.
spirurid – A worm, transmitted by mosquitoes or ticks, that may cause skin sores or infect the stomach lining, body cavity, or blood vessels.
splay leg – A leg or pelvic socket deformity causing the legs to spread out (splay).
spleen – A glandlike, lymphoid organ that is part of the immune system and that stores blood cells and produces some types of white blood cells.
splint – A rigid device used to prevent motion of a joint or of the ends of a fractured bone.
sporadic – Happening or appearing at irregular intervals.
spore – A reproductive cell, produced by bacteria or fungi, capable of developing into a new individual without fusing with another reproductive cell.
sporocyst – The first sac-like reproductive stage in many parasitic flatworms that buds off cells.
sporotrichosis – An infectious disease caused by a yeast-like organism that affects many species, including humans, and that often takes the form of localized, ulcerated skin sores.
spot-on – A solution of active ingredients for application to the skin which typically contains a cosolvent and a spreading agent to ensure that the product is distributed to the entire body.
squamous – Referring to the portion of the epithelium (skin) composed of flat, plate-like cells.
squamous cell carcinoma – A form of skin cancer that usually originates in sun-damaged areas.
stamina – Endurance.
star-gazing – A sign of neurologic disease in which the neck is twisted backward and the animal appears to be looking up into the sky.
stenosis – A constriction or narrowing of a duct or passage; an obstruction.
stereotypic behavior – Repetitious, relatively unvaried actions that have no obvious purpose or function.
stethoscope – An instrument used to magnify sounds produced within the body in order to determine health or diagnose disease.
stifle joint – Knee joint; the tendons, ligaments, and other tissues that connect the upper and lower long bones of the rear leg.
stillbirth – Unintentional death of the fetus in the uterus.
stimulant – A drug or other agent that produces an increase in function of an organ or body part.
stimulation – To cause physical reaction in something such as a nerve or organ.
stimulus – An agent or condition that elicits a reaction or response from an organism.
stomatitis – Inflammation of the mouth.
strain – A group of organisms of the same species, having distinctive characteristics but not usually considered a separate breed or variety.
strike – Maggot infestation, or myiasis.
stunting – A reduction in overall growth or progress.
stye – An infection of one or more of the glands at the edge of the eyelid or under it.
subcutaneous – Located just beneath the skin.
subcutis – The innermost of the 3 layers of the skin.
subspectacle abscessation – A common bacterial eye infection in snakes.
substrate – Ground covering such as newsprint, sand, peat moss, potting soil, wood shavings, or cypress mulch that are used to cover the bottom of cages for animals such as rodents or reptiles.
subvalvular – Located below one of the heart valves.
superficial – Located at the surface, or only affecting the surface.
superficial flexor tendon – A tendon that flexes the joints of the lower leg.
supplement – Something added to complete a thing, make up for a deficiency, or extend or strengthen the whole.
supportive care – A wide range of nonspecific treatments for sick or injured animals designed to relieve the signs of illness and that may include injectable fluids, supplemental feeding, heat, or removal of stress.
suppression – The reduction or stoppage of a normal bodily function.
supravalvular – Located above one of the heart valves.
surgery – Medical procedure to treat injury or disease involving an operation, such as removal or replacement of a diseased organ or tissue.
susceptibility – The likelihood of being affected or infected; vulnerability.
suspension – A dispersion of insoluble or poorly soluble drug particles in a liquid.
suspensory ligament – A ligament that provides support for the fetlock joint in horses.
suture – Any of the fine threads of specialized material used surgically to close a wound or join tissues; also the act of surgically closing a wound or joining tissues using a stitch or stitches.
syndrome – A group of signs that occur together and signal a particular abnormal condition.
synostosis – An abnormality in which 2 adjacent bones, such as vertebrae, fuse together.
synovial fluid – Fluid contained within a joint cavity that helps lubricate the joint.
synovial membrane – Membrane surrounding a joint between bones.
systemic – A disease or condition that affects or spreads throughout the entire body rather than being confined to a single location. Also called generalized.
systole – The second half of the heartbeat, characterized by the sound of the aortic and pulmonary valves closing, when the ventricles contract.


T cell – A type of white blood cell that participates in immune responses to infections and other diseases.
T3, T4 – Two iodine-containing hormones produced by the thyroid gland that act on many cellular processes to regulate metabolic rate.
tablet – A solid pellet made up of one or more compressed powdered drugs and perhaps fillers to be taken by mouth.
tachycardia – A rapid heartbeat.
tarsal joint – The hock, or ankle joint of the lower rear leg.
tarsal – Of, relating to, or situated near the bones of the ankle.
tartar – A hard deposit of organic material that forms on teeth.
temperate – Mild or restrained in behavior or attitude. As refers to climate, neither very hot nor very cold.
tendinitis – Inflammation of a tendon.
tendon – An inelastic band of tough fibrous connective tissue attaching a muscle to a bone or other part.
tension pneumothorax – A buildup of air in the space between the lungs and the chest wall; can lead to collapse of a lung.
tentative diagnosis – Early, most likely diagnosis based on the history, physical examination, and signs of a disorder.
teratogen – Agents or factors that cause or increase the incidence of a congenital defect.
terrestrial – Living on the ground or underneath its surface.
testes – The reproductive organs in a male vertebrate, which produce sperm and the hormone testosterone.
tetanus – An often-fatal disease characterized by spastic contraction of muscles and caused by a toxin produced by Clostridium tetani bacteria. Also called lockjaw.
tetany – Continuous, spastic contraction of muscles, causing rigidity of limbs.
tetralogy of Fallot – A complex congenital heart defect that produces a bluish tinge to skin and membranes caused by insufficient oxygen in the blood.
therapy – Treatment for an illness.
thermography – An imaging technique that records the heat emitted by bodies as infrared radiation; used to diagnose musculoskeletal disorders.
third eyelid – See nictitating membrane.
third phalanx – The outermost bone of a finger or toe.
thoracentesis – Procedure in which a needle is inserted into the chest cavity to withdraw excess fluid.
thoracic – Of, relating to, or situated in or near the chest (thorax).
thorax – The chest cavity, encased by the ribs and containing the heart, lungs, and other organs.
thrombocyte – See platelet.
thrombopoietin – A hormone that regulates the production of blood platelets.
thrombosis – Obstruction of an artery by a blood clot.
thrombus – A blood clot formed in an artery or vein, frequently causing blockage of the blood vessel.
thymus – A gland in the upper chest or the base of the neck that is the site of maturation of some types of lymphocytes, a class of white blood cell.
thyroid gland – An endocrine organ in the base of the neck that regulates metabolism.
thyroid hyperplasia – Enlargement of the thyroid gland. Also known as goiter.
tick – Parasitic invertebrates with 8 legs that suck blood and can transmit several diseases.
tick fever – See Rocky Mountain spotted fever.
tissue – Interconnected cells that perform a similar function within an organism.
tonometer – A device for measuring pressure, particularly pressure inside the eye.
tonsillitis – Inflammation of the tonsils.
tonsil – A small mass of lymphoid tissue in the throat.
topical – Involving local application to a part of the body, especially on the skin; for instance, a topical ointment.
torpor – A state of deep unconsciousness, usually brought on as a result of environmental conditions such as low temperature.
torticollis – A twisting of the neck to one side, resulting in the head being tilted; can be caused by an ear infection or neurologic disease. Also called wry neck.
toxemia – A condition brought on by toxins in the blood, especially those produced by bacteria or a metabolic disturbance.
toxic – Containing or being a toxin; poisonous.
toxicant – A toxic substance.
toxicity – The degree to which something is poisonous.
toxicology – The branch of science that studies how poisons affect animals and people and how they respond to poisons.
toxicosis – Disease or condition resulting from poisoning.
toxin – A poisonous material; most often used to describe poisons produced by plants, animals (such as venomous snakes), and some bacteria.
toxoid – A substance that has been treated to destroy its toxic properties but retains the capacity to stimulate production of antibodies that can neutralize the original toxin.
toxoplasmosis – Infection by Toxoplasma microorganisms, which can cause serious damage to the central nervous system, especially in young animals.
trachea – The thin-walled, cartilaginous tube that connects the throat to the lungs. Also called the windpipe.
tracheal intubation – Insertion of a tube into the trachea to help an animal breathe or to administer anesthesia.
tracheobronchitis – Inflammation of the trachea and large airways (bronchi).
tracheostomy – An emergency procedure for inserting a tube through the neck into the trachea to allow breathing.
tranquilizer – Any of a class of drugs used to produce a calming or soothing effect.
transdermal – Describes a medication delivery form that is absorbed through the skin into the bloodstream, such as a patch or an ointment.
transformation – The 2-step process of development of cancerous cells from healthy cells, consisting of initiation and promotion.
transfusion – The transfer of whole blood or blood products, such as packed red blood cells, from one individual to another.
transmission – The passing of an infection from one individual to another.
trauma – Damage to living tissue caused by an outside source; a wound.
trematodes – Parasitic flatworms.
treponematosis – Infection by bacteria of the genus Treponema, which includes syphilis.
trichinellosis – A parasitic disease caused by a type of roundworm, transmittable to humans and often associated with eating undercooked pork. Also called trichinosis.
tricuspid valve – The valve between the right chambers of the heart, through which blood flows from the right atrium to the right ventricle.
trocarization – A technique used to relieve the pressure in the abdomen when it becomes distended with gas due to an intestinal blockage.
tube feeding – Delivery of nutrients, either a special liquid formula or pureed food, through a tube advanced through the nose or mouth into the stomach.
tuberculosis – Disease of many animal species and humans caused by infection with bacteria of the genus Mycobacterium, which typically affects the respiratory system.
tularemia – A highly contagious bacterial infection found especially in wild rabbits and rodents that may also affect humans, and which may be transmitted by ticks or direct contact with an infected animal.
tumor – An abnormal, usually well defined, mass of tissue within an animal; can be either malignant (cancerous) or benign.
tympanic bullae – The round bones behind the ears.
Tyzzer’s disease – A common infection of rabbits and rodents, caused by Clostridium piliforme bacteria, that typically affects the digestive system. Other species are occasionally affected.


ubiquitous – Existing everywhere.
udder – Another term for the mammary glands of farm animals, including cows, pigs, and horses.
ulcer – A sore of the skin or of a mucous membrane (for instance, the mouth or stomach lining) characterized by erosion and loss of surface tissue.
ulcerate – To develop an ulcer.
ulcerative dermatitis – A skin disorder characterized by formation of ulcers in multiple locations; can be a result of itching and scratching caused by another condition.
ulna – One of the 2 long bones of the lower part of the front leg.
ultrasonography – A diagnostic test that uses a machine which emits ultrasonic sound waves, or sounds above the range that humans can hear, to produce a 2-dimensional image of the inside of a body cavity.
ultraviolet (UV) radiation – Light energy radiating from the sun that is not visible to the human eye and that can cause sunburn and increase the risk of skin cancer.
umbilical – Related to or situated in the umbilical cord, the navel, or the area surrounding the navel.
umbilical cord – The flexible tube connecting the fetus to the placenta, through which nutrients are delivered and waste is expelled.
unconscious – Lacking awareness and the capacity for sensory perception; not conscious.
unthriftiness – Failure of a young animal to grow or gain weight at a normal rate in spite of an adequate diet and absence of obvious illness.
upper airways – The portion of the respiratory tract that extends from the nostrils or mouth through the throat (pharynx).
urate – A salt formed from uric acid. See uric acid.
uremia – A buildup of toxic chemicals in the blood that occurs when the kidneys are not functioning properly.
ureter – The narrow tube that connects the kidney to the bladder.
urethra – The tube from the urinary bladder through which urine exits the body.
uric acid – A weak acid present in the urine, which can lead to gout or other disorders in birds if it builds up to high levels.
urinalysis – Laboratory analysis of urine, used to aid in the diagnosis of disease.
urinate – To expel liquid waste from the body by contracting the urinary bladder.
urine scalding – Skin inflammation caused by prolonged contact with urine.
urogenital tract – Relating to or involving the organs of the urinary tract and the reproductive system.
urolith – A buildup of mineral salts in any part of the urinary tract; also called a urinary calculus or stone.
urolithiasis – A condition brought on by the formation of stones (calculi) in the urinary system of an animal.
urticaria – See hives.
uterus – The organ of the female reproductive system in which the fetus develops.
uvea – The middle layer of the eye, which includes the iris and the muscles that control it.
uveitis – Inflammation of the uvea.


vaccination – The administration of a substance to produce immunity against a specific disease; immunization.
vaccine – A product, including dead or weakened forms of an infectious agent or molecules that are part of the agent, that prompts the immune system to develop defenses against that specific organism.
vagina – The lubricated muscular tube of female mammals that connects the cervix to the vulva, forming the external opening of the genitals.
valve – A membranous structure that closes to prevent the backward flow of material through a canal or passage.
valvular disease – Disease resulting in failure of the heart valves to open or close properly.
vascular – Of, characterized by, or containing vessels that carry fluids, such as blood or lymph, through the body of an animal.
vascular network – The collection of vessels that carry or circulate bodily fluids.
vasculitis – Inflammation of the blood vessels.
vasodilator – Any of a class of drugs intended to lower blood pressure by widening blood vessels, thus increasing blood flow.
vector – An organism, such as a tick or mosquito, that carries an infectious agent between susceptible animals. A vector may also be mechanical (nonliving), such as clothing or equipment.
vein – Any of the system of blood vessels that carry blood toward the heart.
venae cavae – The 2 largest veins, which return blood from the body to the right atrium.
venereal disease – A contagious disease typically spread through sexual activity.
venom – A poisonous fluid injected by the bite or sting of an animal.
venous dilator – A drug that dilates the veins coming to the heart and increases the amount of blood that enters the heart.
ventricle – Either of the 2 lower chambers of the heart.
ventricular fibrillation – A common arrhythmia of the heart characterized by chaotic, ineffective contraction of the heart muscle.
vertebra – Any of the bones forming the spinal column.
vertebrate – An animal with a backbone, such as fish, reptiles, mammals, and birds.
vesicle – A small, raised area of skin, containing fluid; blister.
vesicular stomatitis – An acute viral disease of horses and pigs, transmitted by mosquitoes and other insects and signaled by excessive drooling, loss of appetite due to mouth blisters, and lameness due to foot ulcers.
vestibular system – The organs in the inner ear that control balance.
veterinarian – An individual trained and licensed to treat the medical conditions of animals; a doctor of veterinary medicine.
veterinary dermatologist – A veterinarian specializing in the treatment of skin disorders.
veterinary family practice – Also known as “bond-centered practice,” in which the veterinarian establishes a lifelong relationship with families and their animals and cares not only for the medical welfare of the animal, but also for the social health of its family.
vipers – A group of highly poisonous snakes whose long fangs fold back when not in use.
viral – Of, relating to, or caused by a virus.
virus – A tiny infectious agent consisting of a genetic material (RNA or DNA) in a protein coat, which relies on host cells to reproduce.
visceral – Relating to or affecting one or more of the soft internal organs of the body, especially those within the abdominal cavity.
visceral gout – An inflammatory buildup of uric acid metabolites in the internal organs of reptiles or birds, leading to pain and discomfort.
visceral leishmaniasis – A chronic, severe disease of humans, dogs, and certain rodents caused by protozoa, characterized by skin lesions, lymph node enlargement, weight loss, anemia, lameness, and kidney failure.
vitamin – Any of a group of compounds that are essential for proper body function and growth.
vitamin D – A fat-soluble vitamin required for normal metabolism of calcium and phosphorus.
volume overload – A form of heart failure that results in an increase in the size of the one or both ventricles, the lower chambers of the heart.
vomit – To expel the contents of the stomach; to throw up.
vulva – The external female reproductive organs.


warm-blooded – An animal that maintains a relatively constant and warm body temperature independent of environmental temperature. Also called homeothermic.
wart – A hard, rough lump growing on the skin.
water mold – An aquatic fungus living chiefly in fresh water or moist soil.
water salinity – A measure of the amount of salt in water.
weaning – The process of getting an infant mammal adjusted to eating food rather than drinking its mother’s milk.
wheal – A localized area of fluid buildup in the skin that may be pale or reddened and may itch; a hive.
white blood cell – Any of a group of infection-fighting blood cells. See leukocyte.
withers – The ridge between the shoulder blades of a horse.
womb – Another word for uterus. See uterus.
worms – Soft-bodied organisms, many of which are parasitic and infect animals and/or humans.


x-ray – A high-energy form of electromagnetic radiation that can be used to produce images that allow a veterinarian to see inside the body; also used to describe the pictures produced by the rays, which are also called radiographs.
x-ray therapy – See radiation therapy.


yeast – A small, single-celled fungus that ferments carbohydrates; some types can infect humans and animals.
yellow fat disease – A condition in cats involving inflammation of the fatty tissue, thought to be due to an excess of unsaturated fatty acids in food combined with a deficiency of vitamin E.


zinc toxicity – A typically chronic form of poisoning caused by consumption of items containing the metal zinc and characterized by lameness and stiffness.
zoonosis – A disease that can be passed from animals to people.
zoonotic risk – The likelihood that a disease will be passed from an animal to people.
zygomycosis – A fungal infection of the lining of the mouth, nasal passages, and tissue beneath the skin, or the sides of the head, neck, and body.