A

Abomasum : The fourth compartment of the ruminant stomach. Called the "true stomach" because this is the compartment where acid digestion occurs.
Acute : A rapid, severe onset of signs.
A.I. (a.i.) : Active ingredient in a pesticide formulation.
Alkaloids : A very broad category of complex organic bases containing nitrogen and usually oxygen. These often have a bitter taste.
Alternate : Leaf arrangement with one leaf per node, at different heights on the stem.
Anorexia : Loss of appetite.
Awn : Slender bristle, usually at the end of a plant organ.
Axial : Associated with branches instead of the main stem.
Axil : Angle formed by the stem and an appendage (e.g., leaf).

B
Basal : Associated with the base of the plant.
Bract : Modified leaf associated with a flower.

C
Calystegine: Class of alkaloids that inhibit glycosidases, allowing buildup of certain cellular products, resulting in dysfunction. These affect many cell types, but can permanently damage nervous tissues (brain, spinal cord).
Calyx (calyces): The outermost organs of a flower; usually green.
Capsule: Dry, multiseeded fruit, usually opening at maturity.
Cardiac glycoside: Sugar-containing compound that affects the heart.
Cholestasis: Accumulation of bile in the liver.
Chronic: Over a period of time. Can refer to prolonged or repeated exposure to toxins or to the progression of clinical signs.
Cirrhosis: Liver disease involving hepatocellular necrosis, replacement of dead tissue with fibrous tissue (fibrosis), and distortion of microscopic structural units and, therefore, their function. Usually affects the organ as a whole (diffuse).
Cleft: Deeply indented; split.
Compound: A leaf structure that is divided into distinct segments (leaflets), which are pinnately (like a feather) or palmately (like an open hand) arranged.
Coumarin: A specific two-ringed organic chemical structure containing oxygen.
Cyanogenic glycoside: A sugar-containing compound that also contains a releasable cyanide group.

D
Diterpene alkaloid: A 20-carbon compound structure including nitrogen; not water-soluble. Often part of the essential oil of the plant. Terpenes are plant equivalents of steroids.

E
Edema: Accumulation of fluid within tissues, usually resulting in swelling.
Endophyte: One organism that lives within another. In these instances, a fungus that lives within its plant host, inseparable.
Euthanasia: An induced, easy or painless death.

F
Forb: Any nonwoody plant (herb) other than a grass.

Furocoumarin: Psoralen. A multi-ringed organic chemical that increases the light sensitivity (primary photosensitization) of the skin.

G
Gastroenteritis: Inflammation of the lining of the gastrointestinal tract, often accompanied by outward signs of abdominal pain and diarrhea, sometimes with evidence of blood.
Glycoalkaloid: Sugar-containing alkaloid.
Glycoside: Sugar-containing chemical compound.
Gypsiferous: High in sulfate, as a soil, or water.

H
Hepatic: Relating to the liver.
Hepatotoxic: Toxic to the liver.
Hilum (hilus): Scar on the seed at its point of attachment.
Hypocalcemia: Abnormally low blood calcium.
Hypoglycemia: Abnormally low blood sugar.

I

J
Jaundice: Bile accumulation in the blood, which results in an abnormal yellow color of the skin, mucous membranes, eyeballs and/or fat.
Jugular distension: Bulging of the major veins in the neck, a sign of excessive blood pressure.

K

L
Leaflet: One segment of a compound leaf.
Lectin: Toxalbumin; a plant protein with attached sugars (glycoprotein) that interferes with basic cellular function throughout the body.
Legume: 1. Member of family Leguminosidae. 2. Seed pod typically produced by members of that family.
Lesion: Injured or abnormal area of tissue.
Lethal dose: The amount of a toxin that causes death (as compared to a toxic dose, which causes only the appearance of signs of poisoning).

M
Mesentery: Membranous fold attaching various organs to the body wall.
Monensin: Ionophore antibiotic that changes the types of microorganisms in the rumen to improve feed efficiency; also selects against thiaminase producing microbes, helping prevent polioencephalomalacia.

N
Narcotic: Substance producing insensibility or stupor.
Necrosis: Tissue death.
Neurotoxic: Poisonous or destructive to nerve tissue.

O
Omasum: Small fermentation compartment of the ruminant stomach between the rumen and abomasum.
Opposite: Leaves arranged two at each node in opposite directions.

P
Palatable: Attractive to eat; tasty.
Panicle: Arrangement of flowers around a central axis with individual stalks supporting each flower.
Petiole: Leaf stalk, attaching it to the stem.
Phorbol ester: Certain plant compounds with complex structures associated with cancer promotion.
Photodynamic: Activated by light.
Photosensitization: Hypersensitivity to light; results in photophobia (shying away from light) and sunburn on light-colored and lightly haired skin; sunburn can progress to the point of sloughing skin. Frequently referred to as "photo."
Photosensitization, hepatogenous: Hypersensitivity to light caused by an agent that damages the liver, impairing its ability to metabolize chlorophyll. A partial breakdown product of chlorophyll (phylloerythrin) then causes photosensitization.
Photosensitization, primary: Hypersensitivity to light caused directly by a toxin itself.
Phytate: Plant acid compound.
Polioencephalomalacia: Degeneration of the grey matter of the brain. Most often associated with sudden dietary changes that shift the rumen microbial population to include a microbe that destroys thiamine. Also produced by ingestion of certain plants that contain a thiaminase.
Prostrate: Lying flat upon the ground. Applies both to plant growth habit and to an animal in a state of absolute exhaustion or weakness (prostration).
Pulmonary adenomatosis: A condition of the lungs in which the tissue becomes thickened and gas exchange can no longer take place. Literally, "glandularization of the lungs." The lung tissue fills with air that cannot escape.
Purgative: Causing evacuation of the bowels.
Pyridine alkaloid: Single-ring compounds containing nitrogen.
Pyrrolizidine alkaloid: Organic structure based on five-membered rings, including nitrogen, which causes progressive liver cirrhosis.

Q

Quinolizidine alkaloid: Organic structure based on six-membered rings including nitrogen causing a variety of effects depending on attached functional groups. Several cause birth defects.

R
Resinoid: One of a wide variety of chemical compounds classified by their physical characteristics on purification. These are solid or semisolid at room temperature and are not water-solubleÑotherwise they may have nothing in common.
Reticulum: Small compartment in the ruminant stomach closely associated with the rumen and with roughage fermentation. The papillae transform into ridges on the interior surface to form a ÒhoneycombÓ configuration.
Rhizomes: Underground modified stems producing leafy shoots above and roots below.
Rosette: Crowded cluster of leaves at ground level radiating from a central root.
Rumen: By far the largest digestive compartment in the ruminant stomach. Its primary function is to house microorganisms for fermentation of roughage. The interior surface is densely covered with papillae (fingerlike projections) that increase its surface area for nutrient absorption.
Rumen stasis: Lack of rumen activity. Usually involves death or inactivity or rumen microbes; also, loss of motility of the rumen walls.

S
Saponin: Sugar-containing sterols that irritate the gastrointestinal tract. When absorbed into the bloodstream, they can cause red blood cell rupture and liver damage.
Serous fluid: Clear body fluids resembling the clear, watery portion of the blood.
Serrate: Saw-toothed; with teeth pointing forward.
Sesquiterpene lactone: Organic compound with a steroidal backbone, nitrogen and oxygen. Usually, dermal and gastrointestinal irritants. Sometimes, allergic sensitizers.
Sessile: Attached directly at the base, with no stalk.
Spike: Flowers arranged around a central axis, with each flower on its own stem. Same as panicle, above.
Stamen: The male organ of the flower, which bears the pollen.
Stocking up: In horses, swelling of the lower legs (peripheral dependent edema).

T
Terminal: Growing at the end of a branch or stem.
Toxic dose: The amount of a toxin needed to induce signs (not necessarily a lethal dose, which causes death).
Tremorgen: Fungal byproduct (mycotoxin) that causes trembling because of neurotoxicity.
Triterpene: Plant version of a steroidal compound. Various effects depending on attached functional groups. Part of the plantÕs essential oil.
Tropane alkaloid: Nitrogen-containing organic ring structure, akin to atropine.
Trypsin inhibitor: Agent that inhibits the digestive enzyme, trypsin. By association, these are expected to inhibit other enzymes as well, disrupting cellular functions.

U

V

W
Winged stem: Stem with a pair of parallel, thin extensions on both sides. Usually the wings are extensions of clasping leaves down the stem.

X

Y

Z