intransitive verb
Definition: To develop a layer of dirt or film on a surface, often seen in liquids.
Example: The pond began to scum over after a few days of warm weather.
noun
Definition: A layer of dirty or unwanted material that forms on the surface of a liquid, or a term used to describe people or things that are considered worthless or despicable.
Example: The pond was covered in a thick layer of scum, making it look uninviting.
transitive verb
Definition: To remove a layer of dirt or unwanted material that forms on the surface of a liquid.
Example: The workers had to scum the pond to keep it clean.