Mushroom
late Middle English (originally denoting any fungus having a fleshy fruiting body): from Old French mousseron, from late Latin mussirio(n- ).
wiktionary
From Middle English muscheron, musseron, from Anglo-Norman musherum, moscheron, from Old French moisseron, of obscure origin: probably derived from Old French mosse, moise(“moss”), as the use first applied to a type of fungus which grows in moss, from Frankish *mosa(“moss”) or Old Dutch mosa(“moss”), akin to Old High German mos(“moss, bog”), Old High German mios(“moss, mire”), Old English mēos(“moss”), Old English mōs(“bog, marsh”), Old Norse mosi(“moss”), Old Norse myrr(“bog, mire”), from Proto-Germanic *musą, *musô, *miuziz(“mosses, bog”), from Proto-Indo-European *mews-(“mosses, mold, mildew”). Displaced native Old English swamm. More at mire. Alternatively, the Old French may be of pre-Roman origin. See Ancient Greek μύκης(múkēs, “mushroom”).
etymonline
mushroom (n.)
a word applied at first to almost any of the larger fungi but later to the agaricoid fungi and especially the edible varieties, mid-15c., muscheron, musseroun (attested 1327 as a surname, John Mussheron), from Anglo-French musherun, Old French meisseron (11c., Modern French mousseron), perhaps from Late Latin mussirionem (nominative mussirio), though this might as well be borrowed from French.
Barnhart says "of uncertain origin." Klein calls it "a word of pre-Latin origin, used in the North of France;" OED says it usually is held to be a derivative of French mousse "moss" (from Germanic), and Weekley agrees, saying it is properly "applied to variety which grows in moss," but Klein says they have "nothing in common." For the final -m Weekley refers to grogram, vellum, venom. Modern spelling is from 1560s.
Used figuratively for something or someone that makes a sudden appearance in full form from 1590s, especially an upstart person or family, one who rises rapidly from a low station in life. In reference to the shape of clouds that rise upward and outward after explosions, etc., it is attested from 1916, though the actual phrase mushroom cloud does not appear until 1955.
mushroom (v.)
"expand or increase rapidly; rise suddenly in position or rank," 1741, from mushroom (n.). Related: Mushroomed; mushrooming.
