A copy given to customer showing who is charging (7)
I believe the answer is:
accuser
'showing who is charging' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'a copy given to customer' is the wordplay.
'copy' becomes 'cc' (short for carbon copy).
'given to' means one lot of letters go next to another.
'customer' becomes 'user' (I've seen this in another clue).
'a'+'cc'+'user'='ACCUSER'
Can you help me to learn more?
(Other definitions for accuser that I've seen before include "One making charges" , "One to point the finger" , "origin of charge?" , "Plaintiff" , "One laying charge of crime" .)