A greenish water vegetation (such as algae), usually found floating on the surface of ponds
Semen.
A layer of impurities that accumulates at the surface of a liquid (especially molten metal or water).
A reprehensible person or persons.
The topmost liquid layer of a cesspool or septic tank.
To remove (something) as scum.
To startscum or savescum.
To remove the layer of scum from (a liquid etc.).
To become covered with scum.
Any of various fresh water plants and algae.
Any of numerous marine plants and algae, such as a kelp.