Nick for every policeman (6)
I believe the answer is:
copper
'policeman' is the definition.
(copper can informally mean a police officer)
'nick for every' is the wordplay.
'nick' becomes 'cop' (both can mean to apprehend or arrest).
'for every' becomes 'per' ('per' means 'for each' or 'for every').
'cop'+'per'='COPPER'
(Other definitions for copper that I've seen before include "bluebottle" , "Coin, policeman or metallic element" , "Metal, Cu" , "An element; small coin" , "Small loose change" .)