in·sin·cere /ˌɪnsɪnˈsɪr, sən-/
1. 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.
2. Disappointing; imperfect; unsound. [Obs.]
To render sleep's soft blessings insincere. --Pope.
Syn: -- Dissembling; hollow; hypocritical; deceptive deceitful; false; disingenuous; untrustworthy.
adj : lacking sincerity; "a charming but thoroughly insincere
woman"; "their praise was extravagant and insincere"