Is it ensure, insure, or assure?
1590s, from Late Latin hyperboreanus, from Latin hyperboreus, from Greek hyperboreos "pertaining to the regions of the far north," from hyper (see hyper-) + Boreas (see Boreal). The Hyperboreans were an imagined Arctic people believed by the ancients to be distinguished by piety and happiness. Middle English had iperborie "the far north of the Earth" (mid-15c.).