the enlarged, esp edible, fleshy fruiting body of a class of fungus, consisting typically of a stem bearing a flattened or domed cap: compare toadstool
informal any fungus
something like a mushroom, e.g. in shape or rapidity of growth
(used before a noun) said of growth, development, expansion, etc: happening rapidly and often suddenly
a pale brownish pink colour
[Middle English musseroun from early French mousseron from late Latin mussirion-, mussirio]