Definition 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: mushrooms and related fleshy fungi (including toadstools, puffballs, morels, coral fungi, etc.)

noun: common name for an edible agaric (contrasting with the inedible toadstool)

verb: grow and spread fast

"The problem mushroomed."

verb: pick or gather mushrooms

"We went mushrooming in the Fall."