1. to be honest and genuine in one's words, feelings, or actions; to speak or act without deception or pretense
You should be sincere when apologizing to someone you've hurt.
Você deve ser sincero quando se desculpar com alguém que magoou.
2. to express oneself truthfully without artificiality or exaggeration
Be sincere about your feelings rather than hiding them.
Seja sincero sobre seus sentimentos em vez de ocultá-los.