Is it ensure, insure, or assure?
c.1200, from Old English gelafian "wash by pouring, pour (water)," possibly an early English or West Germanic borrowing (cf. Dutch laven, German laben) of Latin lavare "to wash," or its Old French descendant, laver. Latin lavare is from PIE *leu(e)- "to wash" (cf. Latin luere "to wash," Greek louein "to wash, bathe," Old Irish loathar "basin," Breton laouer "trough," Old English leaþor "lather").