Charge copper in unusual case (6)
I believe the answer is:
accuse
'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 "Bring a charge" , "Indict, blame wrongdoing on" , "Arraign or indict" , "Charge with, lay blame on" , "From what Zola wrote" .)