Casual member wants back pay (4-5)
I believe the answer is:
part-timer
'casual' is the definition.
(casual or part-time worker)
'member wants back pay' is the wordplay.
'member wants' becomes 'part' (I can't explain this - if you can you should give a lot more credence to this answer).
'back' is a reversal indicator.
'pay' becomes 'remit' (remitting is a kind of paying).
'remit' written backwards gives 'timer'.
'part'+'timer'='PART-TIMER'
Can you help me to learn more?
(Other definitions for part-timer that I've seen before include "Casual worker" , "worker on reduced hours" , "One working less than a full week" , "One working reduced hours" , "One not working the whole week" .)