dross

Noun

WordNet 3.0

worthless or dangerous material that should be removed“there were impurities in the water”Synonyms: impurity
the scum formed by oxidation at the surface of molten metalsSynonyms: slag scoria

Dross \Dross\ (dr[o^]s; 115), n. [AS. dros, fr. dre['o]san to fall. See Dreary.]

1.The scum or refuse matter which is thrown off, or falls from, metals in smelting the ore, or in the process of melting; recrement. [1913 Webster]

2.Rust of metals. [R.] --Addison. [1913 Webster]

3.Waste matter; any worthless matter separated from the better part; leavings; dregs; refuse. [1913 Webster]

All world's glory is but dross unclean.— Spenser.[1913 Webster]

At the devil's booth are all things sold, Each ounce of dross coats its ounce of gold.— Lowell.[1913 Webster]