A person who is very sick or injured and needs frequent care is an invalid. Also, something no longer current or useful is invalid.

The main uses of this word have to do with people and things that don't work very well anymore. A driver's license that has expired is invalid — it needs to be renewed. If you lost your health insurance, it's invalid. People who are called invalids are disabled or incapacitated severely. Be careful with this word, because some think it is inappropriate, since it sounds as if some people are not as valid as others based on physical capability.

Definitions of invalid
  1. adjective
    no longer valid
    “the license is invalid
    having come to an end or become void after passage of a period of time
  2. adjective
    having no cogency or legal force
    invalid reasoning”
    “an invalid driver's license”
    of marriages and offspring; not recognized as lawful
    bad, uncollectible
    not capable of being collected
    fallacious, unsound
    containing or based on a fallacy
    erroneous and usually accidental
    invalidated, nullified
    deprived of legal force
    null, void
    lacking any legal or binding force
    sophistic, sophistical
    plausible but misleading
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    well grounded in logic or truth or having legal force
    of marriages and offspring; recognized as lawful
    reasonable, sensible
    showing reason or sound judgment
    executed with proper legal authority
    effectual, legal, sound
    having legal efficacy or force
    legitimate, logical
    based on known statements or events or conditions
    reasoned, sound, well-grounded
    logically valid
    declared or made legally valid
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  3. noun
    someone who is incapacitated by a chronic illness or injury
    synonyms: shut-in
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    type of:
    diseased person, sick person, sufferer
    a person suffering from an illness
  4. verb
    injure permanently
    synonyms: disable, handicap, incapacitate
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    disable by cutting the hock
    type of:
    injure, wound
    cause injuries or bodily harm to
  5. verb
    force to retire, remove from active duty, as of firemen
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    type of:
    remove from a position or an office
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