The Collaborative International Dictionary of English v.0.48:

Godless \God"less\, a.
   Having, or acknowledging, no God; without reverence for God;
   impious; wicked. -- God"less*ly, adv. -- God"less*ness,
   n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

godless
    adj 1: not revering god [syn: godless, irreverent]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "godless":
   agnostic, atheistic, blasphemous, damned, evil, graceless, hellish,
   impious, infidel, iniquitous, irreligious, lost, nonreligious,
   nullifidian, profane, reprobate, sacrilegious, sceptical,
   shriftless, sinful, un-Christly, unangelic, unbelieving,
   unchristian, unconverted, ungodly, unholy, unredeemed,
   unregenerate, unreligious, unrighteous, unsaintly, wicked