Real Dictionary

invalid
adjective: An invalid argument or conclusion is wrong because it is based on a mistake.
adjective: If an action, procedure, or document is invalid, it cannot be accepted, because it breaks the law or some official rule.
countable noun: An invalid is someone who needs to be cared for because they have an illness or disability.

invalid in American English 1
not well; weak and sickly; infirm
adjective: unable to care for oneself due to infirmity or disability
intransitive verb: to become an invalid
noun: an infirm or sickly person
transitive verb: to affect with disease

invalid in American English 2
not valid; having no force; null or void
adjective: not valid; without force or foundation; indefensible

invalid in British English 1
to cause to become an invalid; disable
adjective: incapacitated or disabled by injury, sickness, etc
noun: a person with disablement or chronic ill health

invalid in British English 2
adjective: not valid; having no cogency or legal force