Unctuous/ˈʌŋktʃuəs/ Definition 1 of 2Pro Tip 1/3Insincerity Unctuous behavior often implies dishonesty or pretending to be nice. His unctuous compliments felt empty and deceitful. Pro Tip 2/3Hidden Motives The word is used when someone is overly friendly for self-serving reasons. The salesman's unctuous demeanor made me skeptical. Pro Tip 3/3Positive to Negative 'Unctuous' often starts with a positive impression then shifts to a negative feeling. I was put off by his unctuous charm; it seemed fake.