Inability

from WordNet (r) 3.0 (2006)

inability
    n 1: lack of ability (especially mental ability) to do something
         [ant: {ability}, {power}]
    2: lacking the power to perform [syn: {inability}, {unfitness}]
       [ant: {ability}]

from The Collaborative International Dictionary of English v.0.48

Inability \In`a*bil"i*ty\, n. [Pref. in- not + ability: cf. F.
   inhabilet['e]. See {Able}, and cf. {Unable}.]
   The quality or state of being unable; lack of ability; lack
   of sufficient power, strength, resources, or capacity.
   [1913 Webster]

         It is not from an inability to discover what they ought
         to do, that men err in practice.         --Blair.

   Syn: Impotence; incapacity; incompetence; weakness;
        powerlessness; incapability. See {Disability}.
        [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

46 Moby Thesaurus words for "inability":
      disability, disablement, disqualification, imbecility, inadeptness,
      inadequacy, inaptitude, inaptness, inattentiveness, incapability,
      incapacitation, incapacity, incompetence, incompetency,
      indexterity, ineffectiveness, ineffectuality, ineffectualness,
      inefficiency, ineptitude, ineptness, infancy, inferiority,
      insufficiency, legal incapacity, maladjustment, maladroitness,
      mediocrity, minority, pedestrianism, rustiness, skill-lessness,
      thoughtlessness, unaptness, uncleverness, undeftness,
      undexterousness, undextrousness, unfitness, unfittedness,
      unintelligence, unproficiency, unschooledness, unskillfulness,
      untrainedness, wardship