See unctuous in Webster's New World College Dictionary
adjective
of, like, or characteristic of an ointment or unguent; oily or greasy
made up of or containing fat or oil
like oil, soap, or grease to the touch: said of certain minerals
soft and rich: said of soil
plastic; moldable
characterized by a smug, smooth pretense of spiritual feeling, fervor, or earnestness, as in seeking to persuade; too suave or oily in speech or manner
Characterized by affected, exaggerated, or insincere earnestness: “the unctuous, complacent court composer who is consumed with envy and self-loathing”(Rhoda Koenig).
Having the quality or characteristics of oil or ointment; slippery.
Containing or composed of oil or fat.
Abundant in organic materials; soft and rich: unctuous soil.