Cunning tramp, heading off (4)
I believe the answer is:
arch
'cunning' is the definition.
(arch can mean cunning or tricksy)
'tramp heading off' is the wordplay.
'tramp' becomes 'march' (I've seen this in other clues).
'heading off' means to remove the first letter.
'march' with its first letter taken off is 'ARCH'.
(Other definitions for arch that I've seen before include "Mischievous - shrewd" , "one under a foot?" , "Char the curved structure" , "Way though - on foot!" , "Vaulted opening" .)