adjective
unctuous
UNGK-choo-us/ˈʌŋktʃuəs/
Excessively flattering in a smug or insincere way.
The unctuous employee flatters the manager with an ingratiating smile.

Etymology
A greasy or anointing quality became a figurative smoothness in overly flattering behavior.
More examples
- His unctuous praise makes her suspicious.
- She dislikes the unctuous sales pitch.
Forms
unctuous
Similar words
- sycophantic
- Flattering a powerful person to gain advantage.
- smarmy
- Informally describes an offensively ingratiating manner.