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Synonyms for Authentic (same or very similar meaning)

WordNet sense 1 (conforming to fact and therefore worthy of belief):

WordNet sense 2 (worthy of trust or belief):
trustworthy, trusty

WordNet sense 3 (not counterfeit or copied):
bona fide, unquestionable, veritable

WordNet sense 4 (not fake or counterfeit):
echt, genuine

From the ODE community, based on WordNetadd/edit