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scum
noun
°A layer of impurities that accumulates at the surface of a liquid (especially molten metal or water).
°A greenish water vegetation (such as algae), usually found floating on the surface of ponds.
verb
°To remove the layer of scum from (a liquid etc.).
°To remove (something) as scum.
synonyms: dross, impurity|impurities, cinder, scoriae more» , slag, bastard