mordant (adj.)

late 15c., "caustic" (of words, speech), from Middle French mordant, literally "biting," present participle of mordre "to bite," from Latin mordere "to bite, bite into; nip, sting;" figuratively "to pain, cause hurt," which is perhaps from an extended form of PIE root *mer- "to rub away, harm." Related: Mordantly. The noun sense in dyeing is first recorded 1791; the adjective in this sense is from 1902. Related: Mordancy; mordantly.