toadstool

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An inedible or poisonous fungus with an umbrella-shaped fruiting body.

Century Dictionary and Cyclopedia

1. n. A common name for numerous umbrella-shaped fungi which grow abundantly on decaying vegetable matter. It is usually restricted to the genus Agaricus, but also is extended to various allied fungi, and, still further, is sometimes applied to almost any fungus thiit is large enough to attract general attention, such as Hydnum, Lycoperdon, Morehella, etc. Popularly, the name toadstool is applied only to those fungi supposed to be poisonous, as distinguished from mushrooms, or edible forms, while as a matter of fact all true toadstools, belonging to the genus Agaricus or closely allied genera, are really mushrooms, and may or may not be poisonous. It frequently happens that an edible species is associated with a highly poisonous species, or grows in similar places, and can be distinguished only by a competent authority or by a careful microscopical examination. Also called toad's-cap, toad's-hat, toad's-meat, frogstool.

Wiktionary

1. n. Any inedible or poisonous mushroom, especially an agaric.

GNU Webster's 1913

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

WordNet 3.0

1. n. common name for an inedible or poisonous agaric (contrasting with the edible mushroom)