Of the same origin as claimed; genuine.
The experts confirmed it was an authentic signature.
Conforming to reality and therefore worthy of trust, reliance, or belief.
The report was completely authentic.
(of a Gregorian mode) Having the final as the lowest note of the mode.
Authoritative
To render authentic; to give authority to, by the proof, attestation, or formalities required by law, or sufficient to entitle to credit.
To prove authentic; to determine as real and true.
He didn't manage to authenticate the portrait: it's probably a fake.