a fungus with a round flat head and short stem. Many mushrooms can be eaten. a field mushroom (= the most common type that is eaten, often just called a ‘mushroom’, and often grown to be sold) fried mushrooms cream of mushroom soup Slice the mushrooms and add to the salad. They went into the woods to pick wild mushrooms. see also button mushroom, toadstool Word Origin late Middle English (originally denoting any fungus having a fleshy fruiting body): from Old French mousseron, from late Latin mussirio(n-).