Authentic means truly what it claims to be. An authentic signature, an authentic recipe, authentic materials.
In museums and auctions it is a technical judgement: authenticated means an expert has confirmed it. In food and travel it means not adapted for outsiders, which is a slippery claim — an authentic dish is authentic to somewhere and some period. Of a person, authentic means not pretending. Note authenticity, and authentication, which in computing means proving you are who you say you are.
1adjectiveauthenticTruly what it claims to be.
“The signature is authentic and the rest of the letter is not.”
2adjectiveadaptedNot adapted for outsiders.
“We ate at a tiny family restaurant that served authentic Sichuan food, not the milder version for tourists.”
authentic is a quality of genuineness.
Also accepted in games: genuine
Greek authentikos meant original or done by one's own hand, from autos, self. Something authentic is self-made rather than copied, which is exactly the museum's test.
Ancient Greek
αὐθεντικός — authentic, genuine
Latin
authenticus
Old French
autentique
Middle English
authentik
English, today
authentic
From Middle English authentik, from Old French autentique, from Latin authenticus, from Ancient Greek αὐθεντικός (“authentic, genuine”), from Ancient Greek αὐθέντης (“perpetrator, murderer, absolute ruler”). a doublet of effendi.
Etymology from Wiktionary, CC BY-SA