Definitions
1.adjectiveOf the same origin as claimed; genuine."The experts confirmed it was an authentic signature."
2.adjectiveConforming to reality and therefore worthy of trust, reliance, or belief."The report was completely authentic."
3.adjective(of a Gregorian mode) Having the final as the lowest note of the mode.
4.adjectiveAuthoritative
5.verbTo render authentic; to give authority to, by the proof, attestation, or formalities required by law, or sufficient to entitle to credit.
6.verbTo prove authentic; to determine as real and true."He didn't manage to authenticate the portrait: it's probably a fake."