Source : Webster's Revised Unabridged Dictionary (1913)

Hyperborean \Hy`per*bo"re*an\, a. [L. hyperboreus, Gr. ?; "ype`r
   over, beyond + ?. See {Boreas}.]
   1. (Greek Myth.) Of or pertaining to the region beyond the
      North wind, or to its inhabitants.

   2. Northern; belonging to, or inhabiting, a region in very
      far north; most northern; hence, very cold; fright, as, a
      hyperborean coast or atmosphere.

            The hyperborean or frozen sea.        --C. Butler
                                                  (1633).

Hyperborean \Hy`per*bo"re*an\, n.
   1. (Greek Myth.) One of the people who lived beyond the North
      wind, in a land of perpetual sunshine.

   2. An inhabitant of the most northern regions.

Source : WordNet®

Hyperborean
     n : (Greek mythology) one of a people that the ancient Greeks
         believed lived in a warm and sunny land north of the
         source of the north wind