1398, apparently a fanciful name from M.E. tadde "toad" + stole "stool." Toads themselves were regarded as very poisonous, and this word is popularly restricted to inedible or poisonous fungi, as opposed to mushrooms (e.g. toad-cheese, a poisonous fungi).
Main Entry: toad·stool Pronunciation: -"stül Function: noun : a fungus having an umbrella-shaped pileus :MUSHROOM; especially: a poisonous or inedible one as distinguished from an edible mushroom