Smooth come-back in the role of the Cowardly Lion (4)

I believe the answer is:

oily

I'm a little stuck... Click here to teach me more about this clue!

'smooth' is the definition.
(oily can mean smooth or smarmy)

I don't understand the remainder of the clue.

(Other definitions for oily that I've seen before include "Greasy - obsequious" , "Unpleasantly ingratiating" , "Smooth, ingratiating" , "Smooth; like lubricant" , "Unctuous" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.