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.

Diogenes Hieronymian Hieronymite Timon of Athens absonant afflict ailing anchoress anchorite annulled apoplectic arthritic ascetic bad barren bedridden invalid black blank cartridge bootless cachectic case castrato cloistered monk closet cynic consumptive contradictory contrary to reason counterproductive criminal cripple debilitate debilitated derange desert fathers desert saints devitalize disable disabled disorder drained dud dyspeptic effete empty enervate enervated enfeeble epileptic eremite erroneous etiolated eunuch evil exhausted failing fallacious FALSE fatuitous fatuous faulty feckless feeble flawed frail fruitless futile gelding healthless hermit hermitess homebody hospitalize ill illogical impaired imperfect impotent improper in poor health inaccurate inadequate inane inauspicious inauthentic incapacitate incompetent inconclusive incongruous inconsequent inconsequential inconsistent incorrect incurable indispose ineffective ineffectual inefficacious inexpedient inferior infirm inoperative inpatient irrational isolationist languishing lay up loner loose mad malevolent marabout moribund nonrational nonscientific not following nugacious nugatory null and void of no force outcast outpatient pale paralogical pariah patient peaked peaky peccant pillar saint pillarist reasonless recluse reduce reduced reduced in health repealed repudiated revoked rheumatic run-down seclusionist self-annulling self-contradictory self-refuting senseless shut-in sick sick person sicken sickly sinful sinister solitaire solitary solitudinarian sophistic spastic spurious stay-at-home sterile stylite sufferer terminal case the sick unauthentic unavailing unconnected unfavorable unhealthy unkind unphilosophical unpleasant unreasonable unscientific unskillful unsound untenable untoward untrue useless vain valetudinarian valetudinary vicious victim void weaken weakened weakling weakly wicked with low resistance without reason wrong