Cunning principal (4)

I believe the answer is:

arch

This clue is a double definition.

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

'principal' is the second definition.
(as in arch-enemy)

(Other definitions for arch that I've seen before include "Mischievous - curve" , "Roguish - chief - supporter" , "Construction with a keystone" , "Curved bony structure in the foot" , "Inner part of foot" .)

I've seen this clue in the Sydney Morning Herald.

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