tarnish (v.)
mid-15c. (transitive), from present participle stem of Middle French ternir "dull the luster or brightness of, make dim" (15c.), probably from Old French terne (adj.) "dull, dark," which according to Diez is from a Germanic source cognate with Old High German tarnjan "to conceal, hide," Old English dyrnan "to hide, darken," from Proto-Germanic *darnjaz (see dern), but there are difficulties of form, sense, and date. Intransitive sense from 1670s. Figurative sense is from 1690s. Related: Tarnished; tarnishing.
tarnish (n.)
1713, from tarnish (v.).