1. not genuine or real; fake or false
2. not true to oneself or one’s character; insincere

Examples

• The painting was revealed to be unauthentic after experts examined it.
• His unauthentic smile didn’t fool anyone at the meeting.
• The restaurant served unauthentic Italian food that disappointed tourists.
• She felt unauthentic pretending to enjoy activities she disliked.
• The antique dealer was caught selling unauthentic artifacts.
• His unauthentic accent made it obvious he wasn’t from the South.
• The documentary was criticized for its unauthentic portrayal of historical events.