"of or from the extreme north of the Earth," 1590s, from Late Latin hyperboreanus (adj.), from Latin hyperboreus, from Greek hyperboreos "pertaining to the regions of the far north," from hyper "beyond" (see hyper-) + Boreas, name of the god of the North Wind (see boreal).
The Hyperboreans (Greek Hyperboreoi) were an imagined northern people believed by the ancients to be distinguished by piety and happiness; their land being "beyond" (hence, out of reach of) the North Wind, it was thought to be a blissful paradise. Middle English had iperborie "the far north of the Earth" (mid-15c.).