1. The dross, or recrement, of a metal; also, vitrified cinders.
2. The scoria of a volcano.
(Science: chemistry) Slag furnace, or Slag hearth, a furnace, or hearth, for extracting lead from slags or poor ore. Slag wool, mineral wool. See Mineral.
Origin: Sw. Slagg, or LG. Slacke, whence G. Schlacke; originally, perhaps, the splinters struck off from the metal by hammering. See Slay.