toxin has definitions from the fields of biology,medicine,immunology,pharmacology
[ noun ] (biology,medicine,immunology,pharmacology) a poisonous substance produced during the metabolism and growth of certain microorganisms and some higher plant and animal species

Used in print

(LeRoy Fothergill, "Biological Warfare", in Peter...)

Botulinal toxin , for_example , is several thousand-fold more toxic by this route than when given per os .