scum
n. uncountablen. a layer of dirty bubbles or film on top of a liquid. It is also a very rude name for people you think are dishonest or worthless.
n. a layer of impurities or foul matter that accumulates on the surface of a liquid; by extension, a highly derogatory term for people considered contemptible or socially worthless.
A thick green scum covered the surface of the pond.
The detective looked at the criminals and told them they were the scum of the earth.
Industrial runoff had left a chemical scum along the riverbank, while the local tabloids used the same word to describe the profiteers who owned the factory.
From Middle English scum, scome, skum, skome, scumme, from Middle Low German or Middle Dutch schūme (“foam”), from Old Dutch scūm, from Frankish skūm, from Proto-Germanic skūmaz (“froth, foam”), from Proto-Indo-European (s)kewH- (“to cover, conceal”). Cognate with Dutch schuim (“foam”), West Frisian skuum, German Schaum (“foam”), Danish and Swedish skum (“foam”). Compare also French écume (“scum”), Italian schiuma (“foam”), Saterland Frisian Skuum, Sicilian scuma (“foam”), Walloon schome (“scum, foam”), Lithuanian šamas (“catfish”) and skanus (“tasty”) from the same Germanic source. Related to skim.
Uncountable when referring to the physical film; used as a collective noun when referring to people, often in the phrase 'the scum of'.