The Collaborative International Dictionary of English v.0.48:

Useless \Use"less\, a.
   Having, or being of, no use; unserviceable; producing no good
   end; answering no valuable purpose; not advancing the end
   proposed; unprofitable; ineffectual; as, a useless garment;
   useless pity.
   [1913 Webster]

         Not to sit idle with so great a gift
         Useless, and thence ridiculous.          --Milton.
   [1913 Webster]

   Syn: Fruitless; ineffectual.

   Usage: Useless, Fruitless, Ineffectual. We speak of an
          attempt, effort, etc., as being useless when there are
          in it inherent difficulties which forbid the hope of
          success, as fruitless when it fails, not from any such
          difficulties, but from some unexpected hindrance
          arising to frustrate it; as, the design was rendered
          fruitless by the death of its projector. Ineffectual
          nearly resembles fruitless, but implies a failure of a
          less hopeless character; as, after several ineffectual
          efforts, I at last succeeded.
          [1913 Webster]

                Useless are all words
                Till you have writ "performance" with your
                swords.
                The other is for waiving.         --Beau. & Fl.
          [1913 Webster]

                Waiving all searches into antiquity, in relation
                to this controversy, as being either needless or
                fruitless.                        --Waterland.
          [1913 Webster]

                Even our blessed Savior's preaching, who spake
                as never man spake, was ineffectual to many.
                                                  --Bp.
                                                  Stillingfleet.
          [1913 Webster] -- Use"less*ly, adv. --
          Use"less*ness, n.
          [1913 Webster]

WordNet (r) 3.0 (2006):

useless
    adj 1: having no beneficial use or incapable of functioning
           usefully; "a kitchen full of useless gadgets"; "she is
           useless in an emergency" [ant: useful, utile]

Moby Thesaurus II by Grady Ward, 1.0:

75 Moby Thesaurus words for "useless":
   abortive, aimless, barren, bootless, counterproductive,
   deleterious, detrimental, disadvantageous, disserviceable, effete,
   empty, etiolated, failed, failing, fatuitous, fatuous, feckless,
   fruitless, fustian, futile, good-for-nothing, harmful, hopeless,
   idle, impotent, impracticable, impractical, inadequate, inane,
   incompetent, ineffective, ineffectual, inefficacious, inefficient,
   inept, injurious, inoperative, inutile, invalid, lame, manque,
   meaningless, miscarried, miscarrying, no go, nonfunctional,
   nugacious, nugatory, of no effect, of no force, of no use,
   pointless, prejudicial, purposeless, sterile, stickit, stillborn,
   successless, superfluous, unadvantageous, unavailable, unavailing,
   unfavorable, unfortunate, unpractical, unproductive, unprofitable,
   unpurposed, unrewarding, unserviceable, unsuccessful, unusable,
   unworkable, vain, worthless