No banker would credit it (5)
I believe the answer is:
debit
'no banker' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'would credit it' is the wordplay.
'would credit' becomes 'deb' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'deb'+'it'='DEBIT'
Can you help me to learn more?
(Other definitions for debit that I've seen before include "Opposite of 23 across" , "It's not to one's credit" , "Deduct from account" , "Accounting entry showing sums owing" , "Accounting entry showing amount spent" .)