The Collaborative International Dictionary of English v.0.48:

disability \dis`a*bil"i*ty\, n.; pl. Disabilities.
   1. State of being disabled; deprivation or want of ability;
      absence of competent physical, intellectual, or moral
      power, means, fitness, and the like.
      [1913 Webster]

            Grossest faults, or disabilities to perform what was
            covenanted.                           --Milton.
      [1913 Webster]

            Chatham refused to see him, pleading his disability.
                                                  --Bancroft.
      [1913 Webster]

   2. Want of legal qualification to do a thing; legal
      incapacity or incompetency.
      [1913 Webster]

            The disabilities of idiocy, infancy, and coverture.
                                                  --Abbott.

   Syn: Weakness; inability; incompetence; impotence;
        incapacity; incompetency; disqualification.

   Usage: -- Disability, Inability. Inability is an inherent
          want of power to perform the thing in question;
          disability arises from some deprivation or loss of the
          needed competency. One who becomes deranged is under a
          disability of holding his estate; and one who is made
          a judge, of deciding in his own case. A man may
          decline an office on account of his inability to
          discharge its duties; he may refuse to accept a trust
          or employment on account of some disability prevents
          him from entering into such engagements.
          [1913 Webster]

WordNet (r) 3.0 (2006):

disability
    n 1: the condition of being unable to perform as a consequence
         of physical or mental unfitness; "reading disability";
         "hearing impairment" [syn: disability, disablement,
         handicap, impairment]

Moby Thesaurus II by Grady Ward, 1.0:

97 Moby Thesaurus words for "disability":
   abnormality, acute disease, affection, affliction, ailment,
   allergic disease, allergy, atrophy, bacterial disease,
   birth defect, blight, cardiovascular disease, chronic disease,
   circulatory disease, complaint, complication, condition,
   congenital defect, defect, deficiency disease, deformity,
   degenerative disease, detriment, disablement, disadvantage,
   disease, disorder, disqualification, distemper, drawback, endemic,
   endemic disease, endocrine disease, epidemic disease,
   functional disease, fungus disease, gastrointestinal disease,
   genetic disease, handicap, helplessness, hereditary disease,
   iatrogenic disease, illness, imbecility, impairment, impotence,
   inability, inadequacy, incapability, incapacitation, incapacity,
   incompetence, incompetency, indisposition, inefficiency,
   ineptitude, infancy, infectious disease, inferiority, infirmity,
   insufficiency, legal incapacity, malady, malaise, minority,
   morbidity, morbus, muscular disease, neurological disease,
   nutritional disease, occupational disease, organic disease,
   pandemic disease, pathological condition, pathology, plant disease,
   powerlessness, protozoan disease, psychosomatic disease,
   respiratory disease, rockiness, secondary disease, seediness,
   sickishness, sickness, signs, symptomatology, symptomology,
   symptoms, syndrome, the pip, unfitness, urogenital disease,
   virus disease, wardship, wasting disease, worm disease



Bouvier's Law Dictionary, Revised 6th Ed (1856):

DISABILITY. The want of legal capacity to do a thing.
     2. Persons may be under disability, 1. To make contracts. 2. To bring
actions.
     3.-1. Those who want understanding; as idiots, lunatics, drunkards,
and infants or freedom to exercise their will, as married women, and persons
in duress; or who, in consequence of their situation, are forbidden by the
policy of the law to enter into contracts, as trustees, executors,
administrators, or guardians, are under disabilities to make contracts. See
Parties; Contracts.
    4.-2. The disabilities to sue are, 1. Alienage, when the alien is an
enemy. Bac. Ab. Abatement, B 3; Id. Alien, E: Com. Dig. Abatement , K; Co.
Litt. 129. 2. Coverture; unless as co-plaintiff with her husband, a married
woman cannot sue. 3. Infancy; unless he appears by guardian or prochein ami.
Co. Litt. 135, b; 2 Saund. 117, f, n. 1 Bac. Ab. Infancy, K 2 Conn. 357; 7
John. 373; Gould, Pl. c. 5, Sec. 54. 4. That no such person as that named
has any existence, is not, or never was, in rerum natura. Com. Dig.
Abatement, E 16, 17; 1 Chit. Pl. 435; Gould on Pl. c. 5, Sec. 58; Lawes' Pl.
104; 19 John. 308. By the law of England there are other disabilities; these
are, 1. Outlawry. 2. Attainder. 3. Praemunire. 4. Popish recusancy. 5.
Monachism.
    5. In the acts of limitation it is provided that persons lying under
certain disabilities, such as being non compos, an infant, in prison, or
under coverture, shall have the right to bring actions after the disability
shall have been removed.
    6. In the construction of this saving in the acts, it has been decided
that two disabilities shall not be joined when they occur in different
persons; as, if a right of entry accrue to a feme covert, and during the
coverture she die, and the right descends to her infant son. But the rule is
otherwise when there are several disabilities in the same person; as, if the
right accrues to an infant, and before he has attained his full age, he
becomes non compos mentis; in this case he may establish his right after the
removal of the last disability. 2 Prest. Abs. of Tit. 341 Shep. To. 31; 3
Tho. Co. Litt. pl. 18, note L; 2 H. Bl. 584; 5 Whart. R. 377. Vide
Incapacity.