of no force, weight, or cogency; not valid; weak.-having no force, effect, or efficacy; void; null; as, an invalid contract or agreement.-a person who is weak and infirm; one who is disabled for active service; especially, one in chronic ill health.-not well; feeble; infirm; sickly; as, he had an invalid daughter.-to make or render invalid or infirm.-to classify or enroll as an invalid.