attest, authorize, avouch, certify, confirm, endorse, guarantee, validate, verify, vouch for, warrant
annul, invalidate, render null and void
English Collins Dictionary - English synonyms & Thesaurus
authenticate ( authenticates 3rd person present) ( authenticating present participle) ( authenticated past tense & past participle ) If you authenticate something, you state officially that it is genuine after examining it. verb
He says he'll have no problem authenticating the stamp... V n
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