(in′və·lid) noun
A sickly person, or one disabled, as by wounds, disease, etc.
—adjective
1. Enfeebled by ill health.
2. Pertaining to or for the use of sick persons.
—v.t.
1. To cause to become an invalid; disable.
2. To classify, or release (a soldier, sailor, etc.) from active service as an invalid.
—v.i.
3. To become an invalid.
4. To retire from active service because of ill health: said of soldiers, sailors, etc. [<F invalide <L invalidus not strong]
—in′va·lid·ism noun

(in·val′id) adjective
Having no force, weight, or cogency; null; void. [<L invalidus]
—in·va·lid·i·ty (in′və·lid′ə·tē) noun
—in·val′id·ly adverb