authentic:  Etymologically, something that is authentic is something that has the authority of its original creator. Greek authentikós was a derivative of the noun authéntēs ‘doer, master’, which was formed from autós ‘self’ and the base -hentēs ‘worker, doer’ (related to Sanskrit sanoti ‘he gains’). The adjective’s original meaning in English was ‘authoritative’; the modern sense ‘genuine’ did not develop fully until the late 18th century. (Greek authéntēs, incidentally, was pronounced /afthendis/, and was borrowed into Turkish as efendī, source of English effendi .) => effendi
mid-14c., "authoritative," from Old French autentique (13c., Modern French authentique) "authentic; canonical," and directly from Medieval Latin authenticus, from Greek authentikos "original, genuine, principal," from authentes "one acting on one's own authority," from autos "self" (see auto-) + hentes "doer, being," from PIE *sene- "to accomplish, achieve." Sense of "entitled to acceptance as factual" is first recorded mid-14c.
Traditionally in modern use, authentic implies that the contents of the thing in question correspond to the facts and are not fictitious; genuine implies that the reputed author is the real one; but this is not always maintained: "The distinction which the 18th c. apologists attempted to establish between genuine and authentic ... does not agree well with the etymology of the latter word, and is not now recognized" [OED].