toadstool

noun

1. any of various mushrooms having a stalk with an umbrellalike cap, especially the agarics.
2. a poisonous mushroom, as distinguished from an edible one.
3. any of various other fleshy fungi, as the puffballs and coral fungi.

noun

1. (not in technical use) any basidiomycetous fungus with a capped spore-producing body that is not edibleCompare mushroom (def. 1a)

n.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 inedible or poisonous fungi, as opposed to mushrooms (e.g. toad-cheese, a poisonous fungi).