Reliable account by copper on charge (8)
I believe the answer is:
accurate
'reliable' is the definition.
('accurate' can be similar in meaning to 'reliable')
'account by copper on charge' is the wordplay.
'account' becomes 'ac'.
'by' means one lot of letters go next to another.
'copper' becomes 'cu' (chemical symbol).
'on charge' becomes 'rate' (rate is a kind of charge. I am not sure about the 'on' bit.**).
'ac'+'cu'+'rate'='ACCURATE'
Can you help me to learn more?
(Other definitions for accurate that I've seen before include "Careful, precise" , "Totally correct" , "telling it like it is" , "Correct, free of error" , "carefully and precisely" .)