Dross
WordNet
noun
(1) Worthless or dangerous material that should be removed
"There were impurities in the water"
(2) The scum formed by oxidation at the surface of molten metals
WiktionaryText
Noun
- Waste or impure matter
- Worthless or trivial matter
- Residue that forms on the surface of a metal from oxidation
- The impurities in metal
- A waste product from working with metal