Mushroom meaning : Any of the fleshy fruiting bodies of fungi typically produced above ground on soil or on their food sources (such as decaying wood). A fungus producing such fruiting bodies. Champignon or Agaricus bisporus, the mushroom species most commonly used in cooking. Any of the mushroom-shaped pegs in bar billiards. A concrete column with a thickened portion at the top, used to support a slab. One who rises suddenly from a low condition in life; an upstart. Something that grows very quickly or seems to appear suddenly. To grow quickly to a large size. To gather mushrooms. To form the shape of a mushroom. Having characteristics like those of a mushroom, for example in shape or appearance, speed of growth, or texture.