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]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "sunless":
   Stygian, beamless, black, black as night, caliginous, cheerless,
   dark, dark as night, dark as pitch, darkling, darksome, depressing,
   drear, dreary, dusky, ebon, ebony, eclipsed, funereal, gloomy,
   grey, grim, inky, joyless, night-black, night-clad, night-cloaked,
   night-dark, night-enshrouded, night-filled, night-mantled,
   night-veiled, obfuscated, obscure, obscured, occulted, pitch-black,
   pitch-dark, pitchy, rayless, shadowy, starless, subfusc,
   tenebrious, tenebrose, tenebrous, unhappy, unilluminated,
   unlighted, unlit