Walk miles intercepting ambush (5)
I believe the answer is:
tramp
'walk' is the definition.
(I know that tramp is a type of walk)
'miles intercepting ambush' is the wordplay.
'miles' becomes 'm' (common abbreviation).
'intercepting' means one lot of letters goes inside another (I've seen this in other clues).
'ambush' becomes 'trap' (synonyms).
'm' going within 'trap' is 'TRAMP'.
(Other definitions for tramp that I've seen before include "Take a walk" , "Vagrant, hobo" , "Trudge; vagrant" , "Walk noisily; vagrant" , "Heavy footsteps" .)