n. [ OE. muscheron, OF. mouscheron, F. mousseron; perhaps fr. mousse moss, of German origin. See Moss. ] 1. (Bot.) (a) An edible fungus (Agaricus campestris), having a white stalk which bears a convex or oven flattish expanded portion called the pileus. This is whitish and silky or somewhat scaly above, and bears on the under side radiating gills which are at first flesh-colored, but gradually become brown. The plant grows in rich pastures and is proverbial for rapidity of growth and shortness of duration. It has a pleasant smell, and is largely used as food. It is also cultivated from spawn. (b) Any large fungus developing a visible fruiting body with a stem and cap, usu. of the basidiomycetes; especially one of the genus Agaricus; a toadstool. Several species are edible; but many are very poisonous. The term mushroom is used most often for edible varieties, the poisonous ones being termed toadstools or other names. But this distinction is often ignored. [ 1913 Webster +PJC ]

2. One who rises suddenly from a low condition in life; an upstart. Bacon. [ 1913 Webster ]

a. 1. Of or pertaining to mushrooms; as, mushroom catchup. [ 1913 Webster ]

2. Resembling mushrooms in rapidity of growth and shortness of duration; short-lived; ephemerial; as, mushroom cities. [ 1913 Webster ]

Mushroom anchor, an anchor shaped like a mushroom, capable of grasping the ground in whatever way it falls. --
Mushroom coral (Zool.), any coral of the genus Fungia. See Fungia. --
Mushroom spawn (Bot.), the mycelium, or primary filamentous growth, of the mushroom; also, cakes of earth and manure containing this growth, which are used for propagation of the mushroom. --
mushroom cloud, a cloud of smoke rising and then spreading laterally to take on the shape of a mushroom -- caused by large fires or explosions, esp. nuclear explosions. [ 1913 Webster +PJC ]

v. i. 1. to grow or expand rapidly. [ PJC ]

2. to grow so much and so rapidly as to change qualitatively; used with into; as, a minor border skirmish mushroomed into a full-blown war. [ PJC ]

a. (Bot.) Having a cylindrical body with a convex head of larger diameter; having a head like that of a mushroom. [ 1913 Webster ]