Sincerity is one of the most important virtues that a person can possess. However, in scenarios where being sincere is not possible, it's essential to know the antonyms for "in sincerest". Some of the antonyms for insincere are genuine, honest, truthful, frank, forthright, candid, and authentic. When someone is genuine, they are sincere and honest in their behavior and speech. A truthful person never tells lies and always speaks the truth. A frank person is direct and straightforward in their communication, and someone who is forthright is not afraid to speak their mind. Similarly, a candid person gives their honest opinion without any hesitation. Lastly, authentic individuals always exhibit sincerity and honesty and never pretend to be someone else.