Defy
Middle English (in the senses ‘renounce an allegiance’ and ‘challenge to combat’): from Old French desfier, based on Latin dis- (expressing reversal) + fidus ‘faithful’.
wiktionary
From Old French desfier, from Vulgar Latin *disfidare(“renounce one's faith”), from Latin dis-(“away”) + fidus(“faithful”). Meaning shifted in the 14th century from "be disloyal" to "challenge". Contrast confide, fidelity, faith.
etymonline
defy (v.)
c. 1300, defien, "to renounce one's allegiance;" mid-14c., "to challenge to fight, dare to meet in combat;" from Old French defier, desfier "to challenge, defy, provoke; renounce (a belief), repudiate (a vow, etc.)," from Vulgar Latin *disfidare "renounce one's faith" (in Medieval Latin diffidare), from Latin dis- "away" (see dis-) + fidus "faithful" (from PIE root *bheidh- "to trust, confide, persuade"). By 1670s as "dare (someone) to do something (that the challenger believes cannot or will not be done)."
