Is it ensure, insure, or assure?
Old English geon (adj.) "that (over there)," from Proto-Germanic *jaino- (cf. Old Frisian jen, Old Norse enn, Old High German ener, Middle Dutch ghens, German jener, Gothic jains "that, you"), from PIE pronomial stem *i- (cf. Sanskrit ena-, third person pronoun, anena "that;" Latin idem "the same," id "it, that one;" Old Church Slavonic onu "he;" Lithuanian ans "he").