Insincere :: Insincere (a.) Not being in truth what one appears to be; not sincere; dissembling; hypocritical; disingenuous; deceitful; false; -- said of persons; also of speech, thought; etc.; as, insincere declarations..
Sincere :: Sincere (superl.) Being in reality what it appears to be; having a character which corresponds with the appearance; not falsely assumed; genuine; true; real; as, a sincere desire for knowledge; a sincere contempt for meanness..
Sincere :: Sincere (superl.) Honest; free from hypocrisy or dissimulation; as, a sincere friend; a sincere person..