The Collaborative International Dictionary of English v.0.48:

Caliginous \Ca*lig"i*nous\, a. [L. caliginosus; cf. F.
   caligineux.]
   Affected with darkness or dimness; dark; obscure. [R.]
   --Blount.
   [1913 Webster]

         The caliginous regions of the air.       --Hallywell.
   -- Ca*lig"i*nous*ly, adv. -- Ca*lig"i*nous*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

caliginous
    adj 1: dark and misty and gloomy