scum

A filmy or frothy layer of matter that forms on the surface of a liquid or body of water or on a hard surface.

The refuse or dross of molten metals.

Refuse or worthless matter.

One, such as a person or an element of society, that is regarded as despicable or worthless.

To remove the scum from.

To become covered with scum.

Foam; froth: as, the scum of the sea.

The impurities or extraneous substances which rise to the surface of liquids, as in boiling or fermentation, or which form by other means; also, the scoria of molten metals; hence, by extension, any film or surface of foul floating matter: as, the scum of a stagnant pond.

Refuse; dross; offscourings.

To remove the scum from; clear off the froth, dross, or impurities that have risen to or formed on the surface of; skim.