Military policeman (6)
I believe the answer is:
redcap
'military policeman' is the definition.
(redcap is a kind of military policeman)
This is the entire clue.
(Other definitions for redcap that I've seen before include "MP" , "Member of the military police" , "Carped (anag)" , "Mil. policeman (colloq.)" , "bird!" .)