legendary poisonous tree of Java, 1783, via Dutch, from Malay (Austronesian) upas "poison," in pohun upas "poison tree." As the name of an actual tree (Antiaris toxicaria) yielding poisonous sap, from 1814.
also nicotin, poisonous volatile alkaloid base found in tobacco leaves, 1819, from French nicotine, earlier nicotiane, from Modern Latin Nicotiana, the formal botanical name for the tobacco plant, named for Jean Nicot (c. 1530-1600), French ambassador to Portugal, who sent tobacco seeds and powdered leaves from Lisbon to France 1561. His name is a diminutive of Nicolas (see Nicholas).
c. 1400, in reference to wounds, ulcers, etc., "full of corrupt or poisonous matter," from Latin virulentus "poisonous," from virus "poison" (see virus). Figurative sense of "violent, spiteful" is attested from c. 1600. Related: Virulently.
late 14c., apparently just what it looks like: a fanciful name from Middle English tadde "toad" (see toad) + stole "stool" (see stool). Toads themselves were regarded as highly poisonous, and this word is "popularly restricted to poisonous or inedible fungi, as distinct from edible "mushrooms" [OED]. Compare toad-cheese, a poisonous fungi; toad's meat (1886), a "rustic" term for toadstool.
late 14c., from Old French ellebore, from Latin elleborus, from Greek helleboros, the name given to various plants of both poisonous and medicinal qualities, reputed to cure madness; of uncertain origin. Perhaps literally "plant eaten by fawns," from Greek ellos/hellos "fawn" (from PIE *elno-, extended form of *el- (2) "red, brown," in animal and tree names; see elk) + bora "food of beasts," from bibroskein "to eat" (from PIE root *gwora- "food, devouring"). But Beekes writes, "The traditional etymology seems very doubtful; the word could well be non-IE, i.e. Pre-Greek." Related: Helleboric; helleboraceous.