Etymology
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foam (n.)

Middle English fom, fome (c. 1300), from Old English fam "foam, saliva froth; sea," from West Germanic *faimo- (source also of Old High German veim, German Feim), from PIE root *(s)poi-mo- "foam, froth" (source also of Sanskrit phenah; Latin pumex "pumice," spuma "foam;" Old Church Slavonic pena "foam;" Lithuanian spainė "a streak of foam"). The plastic variety used in packaging, etc., so called from 1937.

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foam (v.)
Old English famgian "to emit foam, to boil," from the source of foam (n.). Sense of "become foamy, to froth" is from late 14c. Transitive sense is from 1725. Related: Foamed; foaming.
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foamy (adj.)
Old English faemig "covered with foam;" see foam (n.) + -y (2). Related: Foaminess.
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Styrofoam (n.)
1950, trademark name (Dow Chemical Co.), from -styr- (from polystyrene) + connective -o- + foam (n.).
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spume (n.)
late 14c., from Old French spume, from Latin spuma "foam" (also source of Italian spuma, Spanish espuma); cognate with Old English fam, Old High German veim "foam" (see foam (n.)).
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pumice (n.)

"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.

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spumoni (n.)
kind of ice cream dessert, 1929, from Italian spumone (singular), spumoni (plural), from spuma "foam" (see spume).
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scum (n.)

early 14c., "froth, foam, thin layer atop liquid" (implied in scomour "scummer, shallow ladle for removing scum"), from Middle Dutch schume "foam, froth," from Proto-Germanic *skuma- (source also of Old Norse skum, Old High German scum, German Schaum "foam, froth"), which is perhaps from PIE root *(s)keu- "to cover, conceal" on the notion of "that which covers the water."

Especially (late 14c.) "impure foam or extraneous substance that rises to the surface when liquid boils." Hence any sort of impure froth, and the sense deteriorated to "film of dirt," then simply "dirt, filth." The meaning "lowest class of humanity" is from 1580s; scum of the Earth is attested by 1712. The Germanic word was adopted in Romanic (Old French escume, Modern French écume, Spanish escuma, Italian schiuma). As a verb, "remove the scum from," late 14c.

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frothy (adj.)
1530s, "full of foam," from froth + -y (2). Meaning "vain, light, insubstantial" is from 1590s. Related: Frothiness.
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spumante (n.)
sparkling white wine from Asti in Piedmont, 1908, from Italian spumante, literally "sparkling," from spuma "foam, froth" (see spume).
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