smirch v.

word-forming element, in English meaning usually "out of, from," but also "upwards, completely, deprive of, without," and "former;" from Latin ex "out of, from within; from which time, since; according to; in regard to," from PIE *eghs "out" (source also of Gaulish ex-, Old Irish ess-, Old Church Slavonic izu, Russian iz). In some cases also from Greek cognate ex, ek. PIE *eghs had comparative form *eks-tero and superlative *eks-t(e)r-emo-. Often reduced to e- before -b-, -d-, -g-, consonantal -i-, -l-, -m-, -n-, -v- (as in elude, emerge, evaporate, etc.).

late 15c., "caustic, biting, severe" (of words, speech), from Old French mordant, literally "biting," present participle of mordre "to bite," from Latin mordēre "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 is first attested in a now-obsolete or archaic sense of "ornamented hooked clasp of a belt or girdle" (mid-14c.), from Old French mordant in this sense. In dyeing, "substance used in fixing colors," it is attested by 1791; as an adjective in dyeing, "having the property of fixing colors," by 1902. Related: Mordancy; mordantly.

"to soil with soot or mud, to sully," now usually figurative, 1590s, from be- + smirch.

Our Gayness and our Gilt are all besmyrcht. ["Henry V," IV.iii.110]

Related: Besmirched; besmirching.