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[syn: ineffective, ineffectual, unable]
The Collaborative International Dictionary of English v.0.48:
Unable \Un*a"ble\, a.
   Not able; not having sufficient strength, means, knowledge,
   skill, or the like; impotent; weak; helpless; incapable; --
   now usually followed by an infinitive or an adverbial phrase;
   as, unable for work; unable to bear fatigue.
   [1913 Webster]
         Sapless age and weak unable limbs.       --Shak.
   [1913 Webster]
WordNet (r) 3.0 (2006):
unable
    adj 1: (usually followed by `to') not having the necessary means
           or skill or know-how; "unable to get to town without a
           car"; "unable to obtain funds" [ant: able]
    2: (usually followed by `to') lacking necessary physical or
       mental ability; "dyslexics are unable to learn to read
       adequately"; "the sun was unable to melt enough snow"
    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:
25 Moby Thesaurus words for "unable":
   ill-qualified, impotent, inadequate, incapable, incapable of,
   incompetent, ineffective, ineffectual, inefficient, inept,
   inferior, maladjusted, not equal to, not up to, powerless,
   unable to, unadapted, unadjusted, unendowed, unequipped, unfit,
   unfitted, ungifted, unqualified, untalented