Etymology: from 1340, "authoritative", from Old French autentique, from Medieval Latin authenticus, from Greek authentikos "original, genuine, principal". Authentic was something that had the authority of its original creator.

Originally from Greek authentikos, it was a derivative of the noun authentes, "doer, master", which was formed from autos, "self" and the base -hentes, "worker, doer, being".

The adjective's original meaning in English was "authoritative"; the modern sense "genuine" did not develop fully until the late 18th century.