—n. 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).
—v.t. 1. to remove the scum from.
2. to remove as scum.