Charge copper in unusual case (6)
I believe the answer is:
Here is my best explanation:
'charge' is the definition.
('accuse' can be a synonym of 'charge')
'copper in unusual case' is the subsidiary indication.
'copper' becomes 'cu' ('Cu' can be a synonym of 'copper').
'in' indicates putting letters inside.
'unusual' indicates an anagram.
'case' anagrammed gives 'acse'.
'cu' going into 'acse' is 'accuse'.
(Other definitions for accuse that I've seen before include "Indict, blame wrongdoing on", "Charge with, indict", "Blame, charge", "Charge with a crime", "Bring a charge", "Put on trial", "Lay blame for wrongdoing on named person", "Charge (someone) with an offence", "Impute fault to, indict" and "Point the finger at".)