The Collaborative International Dictionary of English v.0.48:

Nameless \Name"less\, a.
   1. Without a name; not having been given a name; as, a
      nameless star. --Waller.
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   2. Undistinguished; not noted or famous.
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            A nameless dwelling and an unknown name. --Harte.
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   3. Not known or mentioned by name; anonymous; as, a nameless
      writer."Nameless pens." --Atterbury.
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   4. Unnamable; indescribable; inexpressible.
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            But what it is, that is not yet known; what
            I can not name; 't is nameless woe,I wot. --Shak.
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            I have a nameless horror of the man.  --Hawthorne.
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WordNet (r) 3.0 (2006):

nameless
    adj 1: being or having an unknown or unnamed source; "a poem by
           an unknown author"; "corporations responsible to nameless
           owners"; "an unnamed donor" [syn: nameless,
           unidentified, unknown, unnamed]

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "nameless":
   abominable, anonymous, cryptonymic, cryptonymous, horrible,
   ignotus, incognito, indefinable, indescribable, ineffable,
   inexpressible, inglorious, innominate, little known, no credit to,
   obscure, renownless, repulsive, unacknowledged, uncelebrated,
   undefined, undesignated, undistinguished, unfamed, unglorified,
   unheard-of, unhonored, unidentified, unknown, unmentionable,
   unnamed, unnotable, unnoted, unnoticed, unpopular, unremarked,
   unrenowned, unspeakable, unspecified, unsung, unutterable,
   without a name