Is it ensure, insure, or assure?
1734, from French vampire or German Vampir (1732, in an account of Hungarian vampires), from Hungarian vampir, from Old Church Slavonic opiri (cf. Serbian vampir, Bulgarian vapir, Ukrainian uper), said by Slavic linguist Franc Miklošič to be ultimtely from Kazan Tatar ubyr "witch," but Max Vasmer, an expert in this linguistic area, finds that phonetically doubtful. An Eastern European creature popularized in English by late 19c. gothic novels, however there are scattered English accounts of night-walking, blood-gorged, plague-spreading undead corpses from as far back as 1196. Applied 1774 by French biologist Buffon to a species of South American blood-sucking bat.