Definition of: mushroom

(mush′·rm, -rm) noun
1. A large, rapidly growing fungus of the order Agaricales, consisting of an erect stalk and a caplike expansion: certain poisonous varieties are called toadstools, but the distinction is not scientifically correct. The best–known edible mushrooms are of the genus Agaricus, especially the field mushroom, A. campestris.
2. An object or excrescence of similar shape.
—v.i.
1. To grow or spread rapidly, like a mushroom: The town mushroomed overnight.
2. To expand at one end into a mushroomlike shape: said of bullets.
—adjective
1. Pertaining to or made of mushrooms.
2. Sudden in growth and rapid in decay; ephemeral; upstart. [<OF mouscheron <mousse moss]
AGARIC MUSHROOM
a. Pileus, entire and cut.
b. Stipe in velum.
ca. Ruptured velum.
d. Gills.
cb. Velum forming ring.
da. Cross–section of gill.
e. Mycelium.
f.f. Young mushrooms.