unctuous

unctuous \UNGK-choo-us\, adjective:

1. Of the nature or quality of an unguent or ointment; fatty; oily; greasy.
2. Having a smooth, greasy feel, as certain minerals.
3. Insincerely or excessively suave or ingratiating in manner or speech; marked by a false or smug earnestness or agreeableness.

A warmed, crusty French roll arrives split, lightly smeared with unctuous chopped liver.
-- John Kessler, "Meals To Go: Break from the routine with Hong", Atlanta Journal and Constitution, October 22, 1998

She recalled being offended by the "phoniness" that stemmed from the contradiction between her mother's charming, even unctuous public manner and her anger in private.
-- Daniel Horowitz, Betty Friedan And the Making of 'The Feminine Mystique'

He approached Sean wearing a smile so unctuous it seemed about to slide right off his face.
-- Naeem Murr, The Boy

Unctuous is from Medieval Latin unctuosus, from Latin unctus, "anointed, besmeared, greasy," past participle of unguere, "to anoint, to besmear."