*slag*

n. [ Sw. slagg, or LG. slacke, whence G. schlacke; originally, perhaps, the splinters struck off from the metal by hammering. See Slay, v. t. ] 1. The dross, or recrement, of a metal; also, vitrified cinders. [ 1913 Webster ]

2. The scoria of a volcano. [ 1913 Webster ]

3. (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. [ Webster 1913 Suppl. ]

Slag furnace, or
Slag hearth (Metal.), a furnace, or hearth, for extracting lead from slags or poor ore. --
Slag wool, mineral wool. See under Mineral. [ 1913 Webster ]

v. i. & t. [ imp. & p. p. Slagged p. pr. & vb. n. Slagging. ] (Metal.) To form, or form into, a slag; to agglomerate when heated below the fusion point. [ Webster 1913 Suppl. ]

a. Of or pertaining to slag; resembling slag; as, slaggy cobalt. [ 1913 Webster ]