Unctuous describes someone who acts excessively friendly, agreeable, or flattering in a way that feels fake and insincere. When someone is being unctuous, they're often trying to manipulate you or get something they want by pouring on false charm.

Picture a character in a movie who smiles too widely, agrees with everything the hero says, and offers compliments that sound rehearsed rather than genuine. That overly smooth, oily politeness is unctuousness. You might encounter an unctuous salesperson who calls you “my dear friend” after meeting you two minutes ago, or a classmate who suddenly becomes your “best buddy” right before asking to see your homework.

There's something uncomfortably slick about unctuous behavior, like the person has covered themselves in a layer of fake niceness.

Real kindness and politeness feel natural and honest. Unctuous behavior feels calculated and uncomfortable, like someone wearing a mask of friendliness while planning their next move. When you sense that someone's excessive agreeableness doesn't match their true feelings, you're detecting unctuousness.