The Collaborative International Dictionary of English v.0.48:

Ineffectual \In`ef*fec"tu*al\ (?; 135), a.
   Not producing the proper effect; without effect; inefficient;
   weak; useless; futile; unavailing; as, an ineffectual
   attempt; an ineffectual expedient. --Pope.
   [1913 Webster]

         The peony root has been much commended, . . . and yet
         has been by many found ineffectual.      --Boyle.

   Syn: Inefficient; useless; inefficacious; vain; fruitless;
        unavailing; futile. See Useless, Inefficacious.
        [1913 Webster]

WordNet (r) 3.0 (2006):

ineffectual
    adj 1: not producing an intended effect; "an ineffective
           teacher"; "ineffective legislation" [syn: ineffective,
           uneffective, ineffectual] [ant: effective,
           effectual, efficacious]
    2: producing no result or effect; "a futile effort"; "the
       therapy was ineffectual"; "an otiose undertaking"; "an
       unavailing attempt" [syn: futile, ineffectual, otiose,
       unavailing]
    3: lacking in power or forcefulness; "an ineffectual ruler";
       "like an unable phoenix in hot ashes" [syn: ineffective,
       ineffectual, unable]

Moby Thesaurus II by Grady Ward, 1.0:

117 Moby Thesaurus words for "ineffectual":
   abortive, acarpous, aimless, arid, barren, bootless, borne,
   celibate, childless, counterproductive, desert, desolate, drained,
   dried-up, dry, effete, emasculate, empty, etiolated, exhausted,
   failed, failing, fallow, fatuitous, fatuous, featherweight,
   feckless, forceless, fruitless, futile, gaunt, gelded,
   ill-qualified, impotent, inadequate, inane, incapable, incompetent,
   ineffective, inefficacious, inefficient, infecund, infertile,
   inoperative, invalid, invertebrate, issueless, jejune, lame,
   leached, lightweight, limited, maladjusted, manque, mean,
   meaningless, menopausal, miscarried, miscarrying, narrow, no go,
   no-account, nonfertile, nonproducing, nonproductive, nonprolific,
   not equal to, not up to, nugacious, nugatory, of no account,
   of no effect, of no force, of no use, paltry, pointless, powerless,
   purposeless, set, sine prole, small, spineless, sterile, stickit,
   stillborn, successless, sucked dry, superfluous, teemless, unable,
   unadapted, unadjusted, unauthoritative, unavailable, unavailing,
   uncultivated, unequipped, unfertile, unfit, unfitted, unfortunate,
   unfruitful, unplowed, unproductive, unprolific, unqualified,
   unsown, unsuccessful, untilled, useless, vain, virgin, waste,
   wasted, weak, without any weight, without issue