mor·dant / ˈmôrdnt/ • adj. (esp. of humor) having or showing a sharp or critical quality; biting: a mordant sense of humor.• n. a substance, typically an inorganic oxide, that combines with a dye or stain and thereby fixes it in a material. ∎ an adhesive compound for fixing gold leaf. ∎ a corrosive liquid used to etch the lines on a printing plate.• v. [tr.] impregnate or treat (a fabric) with a mordant.DERIVATIVES: mor·dan·cy / -dnsē/ n.mor·dant·ly adv.