Definitions for toadstoolˈtoʊdˌstul

Random House Webster's College Dictionary

toad•stoolˈtoʊdˌstul(n.)

any of various mushrooms having a stalk with an umbrellalike cap, esp. the agarics.
Category: Fungi
a poisonous mushroom, as distinguished from an edible one.
Category: Fungi
any of various other fleshy fungi, as the puffballs and coral fungi.
Category: Fungi

Origin of toadstool:

1350–1400

Princeton's WordNet

toadstool(noun)
common name for an inedible or poisonous agaric (contrasting with the edible mushroom)

Wiktionary

toadstool(Noun)
Any inedible or poisonous mushroom, especially an agaric.

Origin: Middle English tadde (toad), from Old English tadie, of unknown origin; + Middle English stole (stool), from Old English stol, from Proto-Germanic *stolaz, from Proto-Indo-European *sta-lo-, locative of Proto-Indo-European base *sta- (to stand).

Webster Dictionary

Toadstool(noun)
a name given to many umbrella-shaped fungi, mostly of the genus Agaricus. The species are almost numberless. They grow on decaying organic matter