The Collaborative International Dictionary of English v.0.48:

Sunless \Sun"less\, a.
   Destitute or deprived of the sun or its rays; shaded;
   shadowed.
   [1913 Webster]

         The sunken glen whose sunless shrubs must weep.
                                                  --Byron.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sunless
    adj 1: filled or abounding with clouds [syn: cloud-covered,
           clouded, overcast, sunless]