"given to biting," 1640s (originally figurative, of words, speech, etc.), from Latin mordac-, stem of mordax "biting," from mordēre "to bite," which is perhaps from an extended form of PIE root *mer- "to rub away, harm." Middle English had mordicant (adj.) "corrosive, caustic" (in medicine), early 15c., also mordicative. Related: Mordacity (c. 1600).