Police officer’s coin (6)
I believe the answer is:
copper
This clue is a triple definition!
'police' is the first definition.
(thesaurus)
'officer's' is the second definition.
(copper is a kind of officer)
'coin' is the third definition.
(copper is a kind of coin)
(Other definitions for copper that I've seen before include "Reddish-brown metallic element" , "old tub" , "Coin, policeman or metallic element" , "Chemical element, symbol Cu" , "Reddish metal of a penny" .)