mushroom /ˈmʌʃˌɹuːm/noun 8verb 4adjective 1forms 3 noun8 •Any of the fleshy fruiting bodies of fungi typically produced above ground on soil or on their food sources (such as decaying wood).Some mushrooms are edible whereas others are poisonous, and sometimes they are difficult to tell apart. •A fungus producing such fruiting bodies. •Champignon or Agaricus bisporus, the mushroom species most commonly used in cooking. •Ellipsis of mushroom cloud. •(figurative) Something that grows very quickly or seems to appear suddenly.The craze [hula hoops] began in the U.S.A., and in October the boom crossed the Atlantic and 40 firms sprang into being, some being overnight mushrooms. — 1971 •A concrete column with a thickened portion at the top, used to support a slab. •Any of the mushroom-shaped pegs in bar billiards. •(figurative, no longer used) One who rises suddenly from a low condition in life; an upstart.upstarts […]call in reproach mushrooms — 1627 verb4 •(figurative) To grow quickly to a large size or rapidly increase in scope or scale.The town’s population mushroomed from 10,000 to 110,000 in five years. •To gather mushrooms.We used to go mushrooming in the forest every weekend. •To form the shape of a mushroom.Excessive spot weld time may cause the electrode tips to mushroom, resulting in no focus of current and a weak weld. — 2001 •To form the shape of a mushroom when striking a soft target. adjective[before a noun]1 •Having characteristics like those of a mushroom, for example in shape or appearance, speed of growth, or texture. formsmushroomed · mushrooming · mushrooms