mushroom

Mushroom comes from Middle English muscheron, from Anglo-Norman musherum, from Old French moisseron, likely derived from Old French mosse meaning "moss" — since the fungus was first noticed growing in moss. That French word traces back through Frankish *mosu to Proto-Germanic *musą, and ultimately to a Proto-Indo-European root *mews- meaning "mosses, mold, mildew."

The word entered English through French and Anglo-Norman forms, settling into its current spelling from Middle English muscheron. It eventually displaced the native Old English word for fungus, swamm.

Mushroom is a doublet of both moss and mousse — all three ultimately grow from the same Proto-Indo-European root tied to dampness and soft growth.