One writing a cheque for a back payment (6)
I believe the answer is:
drawer
'one writing a cheque' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'back payment' is the wordplay.
'back' says the letters should be written backwards.
'payment' becomes 'reward' (reward is a kind of payment).
'reward' written backwards gives 'DRAWER'.
'for a' is the link.
Can you help me to learn more?
(Other definitions for drawer that I've seen before include "One sliding into e.g. chest" , "Cheque signatory" , "One signing cheque" , "neither winner nor loser?" , "that's in a chest" .)