Is it ensure, insure, or assure?
Old English wrecan "avenge," originally "to drive, drive out, punish" (class V strong verb; past tense wræc, past participle wrecen), from Proto-Germanic *wrekanan (cf. Old Saxon wrekan, Old Norse reka, Old Frisian wreka, Middle Dutch wreken "to drive, push, compel, pursue, throw," Old High German rehhan, German rächen "to avenge," Gothic wrikan "to persecute"), from PIE root *werg- "to work, to do" (cf. Lithuanian vergas "distress," vergas "slave;" Old Church Slavonic vragu "enemy;" Latin urgere; see urge (v.)). Meaning "inflict or take vengeance," with on, is recorded from late 15c.; that of "inflict or cause (damage or destruction)" is attested from 1817.