Etymology: < French défi, earlier deffy (15th cent. in Littré), < deffi-er , defi-er to defy v.¹Previous versions of the OED give the stress as: deˈfy.

Etymology: Middle English < Old French des- , def- , defier (modern French défier ) = Provençal desfiar , desfizar , Italian disfidare , diffidare , medieval Latin diffīdāre (Du Cange) < Romance *disfīdāre , < dis- prefix privative + *fīdāre to trust, give faith to ( < Latin fīdus faithful). The sense-development appears to have been ‘to renounce faith, alliance, or amity with, declare hostility against, challenge to fight’; the later sense ‘distrust’ found in modern French, and occasionally in English, is, according to Darmesteter, perhaps taken over from Latin diffīdĕre to distrust, of which the Old French representation was difier : see sense 7.

Etymology: The word has all the appearance of being of French origin, but no equivalent Old French defier has yet been recorded, nor is it clear what the etymology of such a form would be. Phonologically, it might answer to Latin dēfæcāre , dēfēcāre (see defecate adj.); but the sense offers difficulties. It has been suggested, however, that if 1b were the starting-point, it might conceivably answer to a late Latin dēfæcāre stomachum (compare dissolvere stomachum Pliny). But the sense-development remains uncertain, and the order here followed is provisional. It may be that ‘dissolve’ was the primary sense.