"northern," late 15c., from Late Latin borealis, from Latin Boreas "north wind," from Greek Boreas, name of the god of the north wind, which is of unknown origin, perhaps related to words in Sanskrit (giri-) and Balto-Slavic (Lithuanian girė, Old Church Slavonic gora) for "mountain" (also "forest") as if "those living beyond the mountains."
1620s, "Northern Lights," literally "northern dawn," said to have been coined by French philosopher Petrus Gassendus (1592-1655) after a spectacular display seen in France Sept. 2, 1621; see aurora + boreal. In northern Scotland and among sailors, sometimes called the dancers, pretty dancers, or merry dancers. Related: Aurora australis (1741).
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.).