adjective (a)

• lacking sincerity(adj.all)

  Example:
  A charming but thoroughly insincere woman.
  Their praise was extravagant and insincere.
  

  Antonym:
  sincere
  

  source: wordnet30
• 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.(adjective)

  source: webster1913