Is it ensure, insure, or assure?
Old English iw, eow "yew," from Proto-Germanic *iwa-/*iwo- (cf. Middle Dutch iwe, Dutch ijf, Old High German iwa, German Eibe, Old Norse yr), from PIE *ei-wo- (cf. Old Irish eo, Welsh ywen "yew"), perhaps a suffixed form of *ei- "reddish, motley, yellow." OED says French if, Spanish iva, Medieval Latin ivus are from Germanic (and says Dutch ijf is from French); others posit a Gaulish ivos as the source of these. Lithuanian jeva likewise is said to be from Germanic. The tree symbolizes both death and immortality, being poisonous as well as long-lived.