adj. & n.
adj. 1 (of sarcasm etc.) caustic, biting. 2 pungent, smarting. 3 corrosive or cleansing. 4 (of a substance) serving to fix colouring-matter or gold leaf on another substance.
n. a mordant substance (in senses 3, 4 of adj.). mordancy n. mordantly adv.
[ ME f. F, part. of mordre bite f. L mordere ]