Definitions of mushroom:

• noun:   fleshy body of any of numerous edible fungi
• noun:   a large cloud of rubble and dust shaped like a mushroom and rising into the sky after an explosion (especially of a nuclear bomb)
• noun:   any of various fleshy fungi of the subdivision Basidiomycota consisting of a cap at the end of a stem arising from an underground mycelium
• noun:   common name for an edible agaric (contrasting with the inedible toadstool)
• verb:   grow and spread fast

  Example: "The problem mushroomed"

• verb:   pick or gather mushrooms

  Example: "We went mushrooming in the Fall"