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 wordplay.
'copper' becomes 'cu' (chemical symbol).
'in' means one lot of letters goes inside another.
'unusual' indicates anagramming the letters.
'case' anagrammed gives 'acse'.
'cu' placed within 'acse' is 'ACCUSE'.
(Other definitions for accuse that I've seen before include "From what Zola wrote", "Indict, blame wrongdoing on", "Make charge against", "Charge with, lay blame on", "Charge with wrong-doing", "Blame, charge", "make charges", "Lay blame for wrongdoing on named person", "Charge (someone) with an offence" and "Impute fault to, indict".)