Source : Webster's Revised Unabridged Dictionary (1913)

Incapacity \In`ca*pac"i*ty\, n.; pl. {Incapacities}. [Cf. F.
   incapacit['e].]
   1. Want of capacity; lack of physical or intellectual power;
      inability.

   2. (Law) Want of legal ability or competency to do, give,
      transmit, or receive something; inability;
      disqualification; as, the inacapacity of minors to make
      binding contracts, etc.

   Syn: Inability; incapability; incompetency; unfitness;
        disqualification; disability.

Source : WordNet®

incapacity
     n 1: lack of intellectual power [ant: {capacity}]
     2: lack of physical or natural qualifications [ant: {capacity}]