Constable (9)
I believe the answer is:
policeman
'constable' is the definition.
(I know that constable can be written as policeman)
This is all the clue.
(Other definitions for policeman that I've seen before include "Rozzer" , "Bobby" , "Member of the force" , "Member of the Garda, say" , "He's responsible for the maintenance of public order" .)