The Collaborative International Dictionary of English v.0.48:

Sightless \Sight"less\, a.
   1. Lacking sight; without sight; blind.
      [1913 Webster]

            Of all who blindly creep or sightless soar. --Pope.
      [1913 Webster]

   2. That can not be seen; invisible. [Obs.]
      [1913 Webster]

            The sightless couriers of the air.    --Shak.
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   3. Offensive or unpleasing to the eye; unsightly; as,
      sightless stains. [R.] --Shak.
      [1913 Webster] -- Sight"less*ly, adv.-
      Sight"less*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sightless
    adj 1: lacking sight; "blind as an eyeless beggar" [syn:
           eyeless, sightless, unseeing]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "sightless":
   ableptical, amaurotic, behind the curtain, behind the scenes,
   benighted, bereft of light, blind, camouflaged, color-blind,
   concealed, dark, dim-sighted, disguised, eyeless, hemeralopic,
   hidden, imperceptible, in darkness, indiscernible, insensible,
   invisible, latent, mind-blind, nyctalopic, out of sight, rayless,
   secret, spiritually blind, stark blind, stone-blind, submerged,
   unapparent, unbeheld, unbeholdable, undiscernible, undiscerning,
   unenlightened, unnoticed, unobserved, unobserving, unperceivable,
   unperceived, unperceiving, unrealized, unseeable, unseeing, unseen,
   unviewed, unwitnessed, viewless, visionless