invalid

from The Century Dictionary.

• Not valid; of no force, weight, or cogency; weak.
• In law, having no validity or binding force; wanting efficacy; null; void: as, an invalid contract or agreement.
• Deficient in health; infirm; weak; sick.
• noun An infirm or sickly person; one who is affected by disease or disabled by any infirmity.
• noun Hence Something that is damaged, or the worse for wear, but not so much as to be wholly unserviceable.
• To affect with disease; render an invalid: chiefly in the past participle.
• To register as an invalid; enroll on the list of invalids in the military or naval service; give leave of absence from duty on account of ill health.
• To cause one's self to be registered as an invalid.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Of no force, weight, or cogency; not valid; weak.
• adjective (Law) Having no force, effect, or efficacy; void; null.
• noun 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.
• adjective Not well; feeble; infirm; sickly.
• transitive verb To make or render invalid or infirm.
• transitive verb To classify or enroll as an invalid.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Not valid; not true, correct, acceptable or appropriate.
• noun One who is confined to home or bed because of illness, disability or injury
• noun Any person with a disability.
• adjective Intended for use by an invalid.
• verb UK To exempt from duty because of injury or ill health.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective no longer valid
• adjective having no cogency or legal force
• verb force to retire, remove from active duty, as of firemen
• verb injure permanently
• noun someone who is incapacitated by a chronic illness or injury