1. Third person singular present indicative of 'ser' (to be) + 'sincero' (sincere). Expresses that someone is being truthful, honest, or genuine.
He is sincere in his intentions.
Ele é sincero em suas intenções.
2. Indicates genuineness or lack of deception in statements or feelings.
She is sincere when she says she cares.
Ela é sincera quando diz que se importa.