c. 1400, prevailen, "be successful; be efficacious," from Old French prevaleir (Modern French prévaloir) and directly from Latin praevalere "be stronger or more able, have greater power," from prae "before" (see pre-) + valere "have power, be strong" (from PIE root *wal- "to be strong"). ... https://www.youtube.com/watch?v=p2cO-3oEkAk