1. [n]  fleshy body of any of numerous edible fungi
2. [n]  a large cloud of rubble and dust shaped like a mushroom and rising into the sky after an explosion (especially of a nuclear bomb)
3. [n]  any of various fleshy fungi of the subdivision Basidiomycota consisting of a cap at the end of a stem arising from an underground mycelium
4. [n]  common name for an edible agaric (contrasting with the inedible toadstool)
5. [v]  grow and spread fast; "The problem mushroomed"
6. [v]  pick or gather mushrooms; "We went mushrooming in the Fall"

Mushroom
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1. \Mush"room\, 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, especially one of the genus
          {Agaricus}; a toadstool. Several species are edible;
          but many are very poisonous.
   2. One who rises suddenly from a low condition in life; an
      upstart. --Bacon.
   

2. \Mush"room\, a.
   1. Of or pertaining to mushrooms; as, mushroom catchup.
   2. Resembling mushrooms in rapidity of growth and shortness
      of duration; short-lived; ephemerial; as, mushroom cities.
   {Mushroom anchor}, an anchor shaped like a mushroom, capable
      of grasping the ground in whatever way it falls.
   {Mushroom coral} (Zo["o]l.), 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.