The Collaborative International Dictionary of English v.0.48:

Cimmerian \Cim*me"ri*an\, a. [L. Cimmerius.] [Written also
   Kimmerian.]
   1. Pertaining to the Cimmerii, a fabulous people, said to
      have lived, in very ancient times, in profound and
      perpetual darkness.
      [1913 Webster]

   2. Without any light; intensely dark.
      [1913 Webster]

            In dark Cimmerian desert ever dwell.  --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Cimmerian
    adj 1: intensely dark and gloomy as with perpetual darkness;
           "the Cimmerian gloom...a darkness that could be
           felt"-Norman Douglas