Longman Dictionary of Contemporary English homepage

invalidate

 verb
     
in‧val‧i‧date [transitive]
1 to make a document, ticket, claim etc no longer legally or officially acceptable:
Failure to disclose all relevant changes may invalidate your policy.
2 to show that something such as a belief or explanation is wrong:
Later findings invalidated the theory.
Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.

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