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1. A filmy or frothy layer of matter that forms on the surface of a liquid or body of water or on a hard surface.
2. The refuse or dross of molten metals.
3. Refuse or worthless matter.
4. Slang One, such as a person or an element of society, that is regarded as despicable or worthless.
v. scummed, scum·ming, scums
To remove the scum from.
To become covered with scum.