Synonyms for Authentic (same or very similar meaning)
WordNet sense 1 (conforming to fact and therefore worthy of belief):
reliableWordNet sense 2 (worthy of trust or belief):
trustworthy, trustyWordNet sense 3 (not counterfeit or copied):
bona fide, unquestionable, veritableWordNet sense 4 (not fake or counterfeit):
echt, genuineFrom the ODE community, based on WordNetadd/edit