Cunning leader vanishing in demo (4)

I believe the answer is:

arch

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

'cunning' is the definition.
(arch can mean cunning or tricksy)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for arch that I've seen before include "one under a foot?" , "Teasing; part of foot" , "Curved bony structure in the foot" , "Playfully superior" , "Embow" .)

I've seen this clue in The Sun, The Independent and The Telegraph.

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.