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.
"type of volcanic rock having a loose or cellular structure," formerly used to smooth parchment or vellum, c. 1400, pomis, from Anglo-French and Old French pomis (13c.), from Late Latin pomicem (nominative pomex, genitive pumicis), from Oscan *poimex or some other dialectal variant of Latin pumex "pumice." This word is from PIE *(s)poi-mo-, a root with connotations of "foam, froth" (see foam (n.)), perhaps because pumice resembled a sort of fossilized foam.
With a wide variety of forms in Middle English, including pumish, pumey. Old English had pumic-stan. As a verb, "to polish or smooth with pumice," early 15c., from the noun.