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1. Waste or impure matter: discarded the dross after recycling the wood pulp.
2. The scum that forms on the surface of molten metal as a result of oxidation.
3. Worthless, commonplace, or trivial matter: "He was wide-awake and his mind worked clearly, purged of all dross" (Vladimir Nabokov).
[Middle English dros, from Old English drōs, dregs.]