invalid Definition

invalid¹
noun

1. Someone who is constantly ill or who is disabled.

Thesaurus: convalescent, valetudinary, patient.

adj

1. Suitable for or being an invalid.

Thesaurus: ailing, disabled, bedridden, frail, ill, infirm, sickly, weak.

verb invalided, invaliding

1a. To discharge (a soldier, etc) from service because of illness;

Form: invalid someone out (usually)
1b. To send (a soldier, etc) home because of illness.

Example: served in Gallipoli before being invalided back home
Form: invalid someone home (usually)
2. To affect with disease.

Derivative: invalidity
noun

Etymology: 17c: from French, from Latin invalidus weak.

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invalid²
adj

1. Said of a document, agreement, etc: having no legal force.
2. Said of an argument, reasoning, etc: based on false reasoning or a mistake and therefore not valid, correct or reliable.

Thesaurus: baseless, irrational, unreasonable, illogical, wrong, unfounded, worthless, fallacious.

Derivative: invalidity
noun

Derivative: invalidly
adverb

Etymology: 17c: from Latin invalidus weak.