| Noun | 1. | toxin - a poisonous substance produced during the metabolism and growth of certain microorganisms and some higher plant and animal speciesricin, ricin toxin - a toxic protein extracted from castor beans; used as a chemical reagent; can be used as a bioweapon; "one milligram of ricin can kill an adult" poison, poisonous substance, toxicant - any substance that causes injury or illness or death of a living organism animal toxin, zootoxin - a toxin resembling bacterial toxins in its antigenic properties that is found in the fluids of certain animals bacterial toxin - any endotoxin or exotoxin formed in or elaborated by bacterial cells cytotoxin - any substance that has a toxic effect on cells endotoxin - a toxin that is confined inside the microorganisms and is released only when the microorganisms are broken down or die exotoxin - a toxin that is secreted by microorganisms into the surrounding medium hepatotoxin - any toxin that affects the liver nephrotoxin - any toxin that affects the kidneys neurolysin, neurotoxin - any toxin that affects neural tissues phytotoxin, plant toxin - any substance produced by plants that is similar in its properties to extracellular bacterial toxin |