Weak, of no force, weight or cogency.

In law, having no force, effect or efficacy; void; null; as an invalid contract or agreement.

A person who is weak and infirm; a person sickly or indisposed.

A person who is infirm, wounded, maimed, or otherwise disabled for active service; a soldier or seaman worn out in service. The hospitals for invalids at Chelsea and Greenwich, in England, are institutions honorable to the English nation.