Is it ensure, insure, or assure?
early 14c., of uncertain origin, perhaps from Scandinavian (cf. Swedish dialectal puta "to be puffed out"), or Frisian (cf. East Frisian püt "bag, swelling," Low German puddig "swollen"); related via notion of "inflation" to Old English ælepute "fish with inflated parts," and Middle Dutch puyt, Flemish puut "frog," from hypothetical PIE imitative root *beu- suggesting "swelling" (see bull (n.2)). Related: Pouted; pouting. As a noun from 1590s.