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REFERENCE

invalid

adj. · v.
US //ˈɪnvəɫəd// in·valid
  1. 1 not legally or logically correct (adj.)
    B1 Intermediate

    not true, correct, or acceptable according to the rules.

    lacking legal force or logical validity; null and void.

    Example

    The website said my password was invalid because I used the wrong characters.

    Example

    The contract was declared invalid by the court because one of the signatures had been forged.

    Usage

    The stress is on the second syllable: in-VAL-id.
    Pitfall
    The password was unvalid.
    The password was invalid.

    The prefix for 'valid' is 'in-', not 'un-'.

  2. 2 to release from duty due to illness (v.)
    C1 Advanced British English Formal

    to officially allow someone to leave the army or a job because they are too sick to work.

    to remove someone from active duty, particularly in a military context, due to injury or chronic ill health.

    Example

    The soldier was invalided out of the army after losing his sight in the war.

    Example

    He was eventually invalided home after contracting a tropical fever that left him unable to perform his duties.

    Usage

    Usually appears in the passive voice as 'to be invalided out'.

    Teacher's tip

    This is a specialized term mostly found in historical or military literature.
Etymology 1

From in- + valid.

Etymology 2

From Middle French invalide, from Latin invalidus (“infirm, weak”), from in- (“not”) + validus (“strong”).

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