The Collaborative International Dictionary of English v.0.48:

Unavailing \Unavailing\
   Ineffective in achieving the desired result; ineffectual;
   futile; of no use; useless; pointless.
   [PJC]

WordNet (r) 3.0 (2006):

unavailing
    adj 1: producing no result or effect; "a futile effort"; "the
           therapy was ineffectual"; "an otiose undertaking"; "an
           unavailing attempt" [syn: futile, ineffectual,
           otiose, unavailing]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "unavailing":
   abortive, aimless, barren, bootless, counterproductive, effete,
   empty, etiolated, fatuitous, fatuous, feckless, fruitless, futile,
   impotent, inadequate, inane, ineffective, ineffectual,
   inefficacious, inoperative, invalid, meaningless, no go, nugacious,
   nugatory, of no force, of no use, pointless, purposeless, sterile,
   superfluous, unavailable, unproductive, useless, vain