mordant (adj.) Look up mordant at Dictionary.com
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.