Is it ensure, insure, or assure?
Old English hwettan, from Proto-Germanic *khwatjanan (cf. Old Norse hvetja "to sharpen, encourage," Middle Low German, Middle Dutch wetten, Old High German wezzan, German wetzen "to sharpen," Gothic ga-hvatjan "to sharpen, incite"), from an adjective represented by Old English hwæt "brave, bold," Old Saxon hwat "sharp," from Proto-Germanic *khwataz, from PIE root *qwed- "sharp" (cf. Sanskrit codati "incites," literally "sharpens"). Figurative sense was in Old English.