Copper assesses clergymen (7)
I believe the answer is:
curates
'clergymen' is the definition.
(curate is a kind of clergyman)
'copper assesses' is the wordplay.
'copper' becomes 'Cu' (Cu is the chemical symbol for copper).
'assesses' becomes 'rates' (rating is a kind of assessing).
'cu'+'rates'='CURATES'
(Other definitions for curates that I've seen before include "Servicemen" , "clerical workers" , "Members of the clergy" , "Clerics" , "Vicars' seconds" .)