dross

American Heritage® Dictionary of the English Language, Fourth Edition

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

Century Dictionary and Cyclopedia

1. n. Refuse or impure or foreign matter which separates from a liquid and falls to the bottom or rises to the top, as in wine or oil or in molten metal; sediment; lees; dregs; scum; any refuse or waste matter, as chaff; especially, and now chiefly, the slag, scales, or cinders thrown off from molten metal.
2. n. In galvano-elect., an alloy of zinc and iron formed in the zinc-bath, partly by the solvent action of the zinc on the iron of the pot, but chiefly from the iron articles dipped, and from the dripping off of the superfluous amalgam as they come from the bath.
3. n. Figuratively, a worthless thing; the valueless remainder of a once valued thing.
4. To remove dross from.
5. To convert (lead) into dross or protoxid by melting in an oxidizing atmosphere. The operation is usually accomplished in a reverberatory furnace.

Wiktionary

1. n. Waste or impure matter
2. n. Worthless or trivial matter
3. n. Residue that forms on the surface of a metal from oxidation
4. n. The impurities in metal
5. n. A waste product from working with metal
6. v. transitive To remove dross from.

GNU Webster's 1913

1. n. The scum or refuse matter which is thrown off, or falls from, metals in smelting the ore, or in the process of melting; recrement.
2. n. rare Rust of metals.
3. n. Waste matter; any worthless matter separated from the better part; leavings; dregs; refuse.

WordNet 3.0

1. n. worthless or dangerous material that should be removed
2. n. the scum formed by oxidation at the surface of molten metals