[mush.room] n [alter. of ME musseroun, fr. MF mousseron, fr. LL mussirion-, mussirio] (1533) 1 a: an enlarged complex aboveground fleshy fruiting body of a fungus (as a basidiomycete) that consists typically of a stem bearing a pileus; esp: one that is edible b: fungus
2: upstart
3: something resembling a mushroom
[2]mushroom vi (1894) 1: to collect wild mushrooms
2. a: to well up and spread out laterally from a central source b: to become enlarged or extended: grow
3: to spring up suddenly or multiply rapidly