Noah Webster's New International Dictionary of the English Language

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

2. (a.) of no force, weight, or cogency; not valid; weak.

3. (n.) A person who is weak and infirm; one who is disabled for active service; especially, one in chronic ill health.

4. (n.) Not well; feeble; infirm; sickly; as, he had an invalid daughter.

5. (v. t.) To make or render invalid or infirm.

6. (v. t.) To classify or enroll as an invalid.