Unionist in outburst over cut leads to banishment (9)
I believe the answer is:
expulsion
'banishment' is the definition.
(expulsion is a kind of banishment)
'unionist in outburst over cut' is the wordplay.
I cannot quite understand how this works, but
'unionist' could be 'u' (abbreviation as in Democratic Unionist Party) and 'u' is found within the answer.
'over' could be 'on' (physically on top of) and 'on' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'leads to' is the link.
Can you help me to learn more?
(Other definitions for expulsion that I've seen before include "Removal, as from school" , "Action of forcing out" .)