Source : Webster's Revised Unabridged Dictionary (1913)

Invalid \In*val"id\, a. [Pref. in- not + valid: cf. F. invalide,
   L. invalidus infirm, weak. Cf. {Invalid} infirm.]
   1. Of no force, weight, or cogency; not valid; weak.

   2. (Law) Having no force, effect, or efficacy; void; null;
      as, an invalid contract or agreement.

Invalid \In"va*lid\ (?; 277), n. [F. invalide, n. & a., L.
   invalidus, a. See {Invalid} null.]
   A person who is weak and infirm; one who is disabled for
   active service; especially, one in chronic ill health.

Invalid \In"va*lid\, a. [See {Invalid}, n.]
   Not well; feeble; infirm; sickly; as, he had an invalid
   daughter.

Invalid \In"va*lid\, v. t.
   1. To make or render invalid or infirm. ``Invalided, bent,
      and almost blind.'' --Dickens.

   2. To classify or enroll as an invalid.

            Peace coming, he was invalided on half pay.
                                                  --Carlyle.

Source : WordNet®

invalid
     adj 1: having no cogency or legal force; "invalid reasoning"; "an
            invalid driver's license" [ant: {valid}]
     2: no longer valid; "the license is invalid"

invalid
     n : someone who is incapacitated by a chronic illness or injury
         [syn: {shut-in}]

invalid
     v 1: force to retire, remove from active duty, as of firemen
     2: injure permanently; "He was disabled in a car accident"
        [syn: {disable}, {incapacitate}, {handicap}]