1326 (implied in
scummer "shallow ladle for removing scum"), from M.Du.
schume "foam, froth," from P.Gmc.
*skuma- (cf. O.N.
skum, O.H.G.
scum, Ger.
Schaum "foam, froth"), perhaps from PIE base
*(s)keu- "to cover, conceal" (see
hide (n.1)). Sense deteriorated from "thin layer atop liquid" to "film of dirt," then just "dirt." Meaning "lowest class of humanity" is 1586;
scum of the Earth is from 1712. Adopted in Romanic, cf. O.Fr.
escume, Mod.Fr.
écume, Sp.
escuma, It.
schiuma. Adj.
scummy first attested 1577; transf. sense of "filthy, disreputable" is recorded from 1932. Slang
scumbag "condom" is from 1967; meaning "despicable person" is from 1971.