slag

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The vitreous mass left as a residue by the smelting of metallic ore.
• transitive & intransitive verb To change into or form slag.

from The Century Dictionary.

• noun A hollow or depression of land.
• To form a slag, or to cohere when heated so as to become a slag-like mass.
• noun The earthy matter separated, in a more or less completely fused and vitrified condition, during the reduction of a metal from its ore.
• noun The scoria of a volcano.
• noun In the puddling process for making wrought-iron, the slag which forms when, as a preliminary step not always taken, air is blown down upon the surface of a charge of melted cask iron in a specially constructed hearth. Silicon is the principal substance removed from the iron, and the slag consists mainly of ferrous silicate.
• In metal: To convert into slag: as, an excess of limestone used as a flux may to a greater or less extent slag the lining of a furnace.
• To cake together as the result of chemical action at a heat lower than that of fusion.

from the GNU version of the Collaborative International Dictionary of English.

• noun The dross, or recrement, of a metal; also, vitrified cinders.
• noun The scoria of a volcano.
• noun (Metal.) A product of smelting, containing, mostly as silicates, the substances not sought to be produced as matte or metal, and having a lower specific gravity than the latter; -- called also, esp. in iron smelting, cinder. The slag of iron blast furnaces is essentially silicate of calcium, magnesium, and aluminium; that of lead and copper smelting furnaces contains iron.
• noun (Metal.) a furnace, or hearth, for extracting lead from slags or poor ore.
• noun mineral wool. See under Mineral.
• verb (Metal.) To form, or form into, a slag; to agglomerate when heated below the fusion point.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Waste material from a coal mine.
• noun Scum that forms on the surface of molten metal.
• noun Impurities formed and separated out when a metal is smelted from ore; vitrified cinders (Wikipedia).
• noun Hard aggregate remaining as a residue from blast furnaces, sometimes used as a surfacing material.
• noun Scoria associated with a volcano.
• noun UK, pejorative, dated A coward.
• noun UK, pejorative A contemptible person, a scumbag.
• noun UK, pejorative A prostitute.
• noun UK, Australia, New Zealand, slang, pejorative A woman (sometimes a man) who has loose morals relating to sex; a slut.
• verb transitive To produce slag.
• verb transitive, with "off" To talk badly about; to malign or denigrate (someone).
• verb intransitive, Australia, slang To spit.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb convert into slag
• noun the scum formed by oxidation at the surface of molten metals