Definitions from Wiktionary ( )

▸ noun:  (uncountable) A layer of impurities that accumulates at the surface of a liquid (especially molten metal or water).
▸ noun:  (uncountable) A greenish water vegetation (such as algae), usually found floating on the surface of ponds
▸ noun:  The topmost liquid layer of a cesspool or septic tank.
▸ noun:  (uncountable, slang, chiefly US) Semen.
▸ noun:  (derogatory, slang) A reprehensible person or persons.
▸ verb:  To remove the layer of scum from (a liquid etc.).
▸ verb:  To remove (something) as scum.
▸ verb:  To become covered with scum.
▸ verb:  (obsolete) To scour (the land, sea, etc.).
▸ verb:  (obsolete) To gather together, as scum.
▸ verb:  (video games, informal) To startscum or savescum.

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