Unctuous
Etymology
From Latin unctus, "anointed," the past participle of unguere, "to anoint or smear with oil" — the same root as "ointment" and "unguent." Its first English sense was literally "oily, greasy." The figurative leap is easy to feel: excessive, slippery flattery is smarmy in the same way oil is, and that slick, false earnestness became the word’s main meaning.
adjective · /UNK-choo-us/
Excessively and insincerely flattering, in an oily, ingratiating way.
What it names
The greasy charm of someone whose warmth is laid on so thick you can feel the calculation behind it.
Example
The salesman’s unctuous compliments about her "impeccable taste" only made her trust him less.
Related idea
Obsequious is fawning through servile eagerness to please; unctuous adds a distinctly oily, self-satisfied smoothness to the flattery.