an infirm or sickly person.

a person who is too sick or weak to care for himself or herself

My father was an invalid the last ten years of his life.

Archaic . a member of the armed forces disabled for active service.

unable to care for oneself due to infirmity or disability

his invalid sister.

of or for invalids

invalid diets.

(of things) in poor or weakened condition

the invalid state of his rocking chair.

to affect with disease; make an invalid

He was invalided for life.

to remove from or classify as not able to perform active service, as an invalid.

British . to remove or evacuate (military personnel) from an active theater of operations because of injury or illness.

to become an invalid.

adjective

sound , valid , worthwhile , worthy , healthy , well

adjective

bad , baseless , fallacious , false , ill-founded , illogical , inoperative , irrational , mad , not binding , not working , nugatory , null , null and void * , reasonless , sophistic , unreasonable , unreasoned , unscientific , unsound , untrue , void , wrong , ailing , bedridden , below par , debilitated , disabled , down , feeble , frail , ill , infirm , laid low , on the sick list , out of action , peaked , poorly , run-down , sick , weak , specious , spurious , inauthentic , null and void , of no efficacy , powerless , unfounded , unlawful , valetudinarian

noun

consumptive , convalescent , incurable , patient , shut-in , sufferer , cripple , feeble , ineffective , infirm , null , sickly , unfounded , unreasonable , useless , valetudinarian , void , weak , worthless