scum

noun

1. a film or layer of foul or extraneous matter that forms on the surface of a liquid.
2. refuse or offscourings.
3. a low, worthless, or evil person.
4. such persons collectively; riffraff; dregs.
5. scoria(def 1).

verb (used with object), scummed, scum·ming.

6. to remove the scum from.
7. to remove as scum.

verb (used without object), scummed, scum·ming.

8. to form scum; become covered with scum.

noun

1. a layer of impure matter that forms on the surface of a liquid, often as the result of boiling or fermentation
2. the greenish film of algae and similar vegetation surface of a stagnant pond
3. Also called: dross, scruff the skin of oxides or impurities on the surface of a molten metal
4. waste matter
5. a worthless person or group of people

verb scums, scumming or scummed

6. (tr) to remove scum from
7. (intr) rare to form a layer of or become covered with scum

n.early 14c. (implied in scummer “shallow ladle for removing scum”), from Middle Dutch schume “foam, froth,” from Proto-Germanic *skuma- (cf. Old Norse skum, Old High German scum, German Schaum “foam, froth”), perhaps from PIE root *(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 1580s; scum of the Earth is from 1712. Adopted in Romanic, cf. Old French escume, Modern French écume, Spanish escuma, Italian schiuma.