The Collaborative International Dictionary of English v.0.48:

Incapability \In*ca`pa*bil"i*ty\, n.
   1. The quality of being incapable; incapacity. --Suckling.
      [1913 Webster]

   2. (Law) Lack of legal qualifications, or of legal power; as,
      incapability of holding an office.
      [1913 Webster]

WordNet (r) 3.0 (2006):

incapability
    n 1: lack of potential for development [syn: incapability,
         incapableness] [ant: capability, capableness,
         potentiality]
    2: the quality of not being capable -- physically or
       intellectually or legally [syn: incapability,
       incapableness] [ant: capability, capableness]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "incapability":
   ad lib, disability, disablement, disqualification,
   extemporaneousness, imbecility, improvisation, inability,
   inadeptness, inadequacy, inaptitude, inaptness, inattentiveness,
   incapacitation, incapacity, incompetence, incompetency,
   indexterity, ineffectiveness, ineffectuality, inefficiency,
   ineptitude, ineptness, infancy, inferiority, insufficiency,
   lack of preparation, legal incapacity, maladjustment,
   maladroitness, mediocrity, minority, nonpreparation,
   nonpreparedness, pedestrianism, planlessness, rustiness,
   skill-lessness, thoughtlessness, unaptness, uncleverness,
   undeftness, undexterousness, undextrousness, unfitness,
   unfittedness, unintelligence, unpreparedness, unproficiency,
   unqualification, unqualifiedness, unreadiness, unschooledness,
   unskillfulness, unsuitability, unsuitableness, unsuitedness,
   untrainedness, unworkmanlike, vulnerability, wardship