slag / slag/ • n. 1. stony waste matter separated from metals during the smelting or refining of ore. ∎  similar material produced by a volcano; scoria.2. Brit., inf., derog. a promiscuous woman.• v. (slagged, slag·ging) [intr.] [usu. as n.] (slagging) produce deposits of slag.DERIVATIVES: slag·gy adj. (-gi·er, -gi·est) .

slag refuse matter from smelting. XVI. — MLG. slagge, perh. f. slagen strike, SLAY1, with ref. to fragments resulting from hammering.