Is it ensure, insure, or assure?
Old English eowu, fem. of eow "sheep," from Proto-Germanic *awi, genitive *awjoz (cf. Old Saxon ewi, Old Frisian ei, Middle Dutch ooge, Dutch ooi, Old High German ouwi "sheep," Gothic aweþi "flock of sheep"), from PIE *owi- (cf. Sanskrit avih, Greek ois, Latin ovis, Lithuanian avis "sheep," Old Church Slavonic ovica "ewe," Old Irish oi "sheep," Welsh ewig "hind").