The process by which air is circulated through or mixed with a substance such as soil or a liquid.
By extension, a process in which other gases (such as carbon dioxide or nitrogen or argon) are circulated through or mixed with a substance (usually liquid), sometimes with the consequence of increasing the transfer of air into the same liquid at the surface due to the induced circulation.
A layer of impurities that accumulates at the surface of a liquid (especially molten metal or water).
Semen.
A greenish water vegetation (such as algae), usually found floating on the surface of ponds
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.