The Collaborative International Dictionary of English v.0.48:

Invalid \In*val"id\, a. [Pref. in- not + valid: cf. F. invalide,
   L. invalidus infirm, weak. Cf. Invalid infirm.]
   [1913 Webster]
   1. Of no force, weight, or cogency; not valid; weak.
      [1913 Webster]

   2. (Law) Having no force, effect, or efficacy; void; null;
      as, an invalid contract or agreement.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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 who is
   unable to care for himself.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Invalid \In"va*lid\, a. [See Invalid, n.]
   Not well; feeble; infirm; sickly; as, he had an invalid
   daughter.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Invalid \In"va*lid\, v. t.
   1. To make or render invalid or infirm. "Invalided, bent, and
      almost blind." --Dickens.
      [1913 Webster]

   2. To classify or enroll as an invalid.
      [1913 Webster]

            Peace coming, he was invalided on half pay.
                                                  --Carlyle.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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    2: no longer valid; "the license is invalid"
    n 1: someone who is incapacitated by a chronic illness or injury
         [syn: invalid, shut-in]
    v 1: force to retire, remove from active duty, as of firemen
    2: injure permanently; "He was disabled in a car accident" [syn:
       disable, invalid, incapacitate, handicap]