Former priest stands up to banishment (5)
I believe the answer is:
exile
'banishment' is the definition.
(exile is a kind of banishment)
'former priest stands up' is the wordplay.
'former' becomes 'ex'.
'priest' becomes 'eli' (I've seen this before).
'stands up' says the letters should be written in reverse (I've seen 'stood up' mean this (in a down clue, letters go up)).
'eli' backwards is 'ile'.
'ex'+'ile'='EXILE'
'to' is the link.
(Other definitions for exile that I've seen before include "Send to live abroad" , "officially banish" , "Person expelled from home country" , "being always away from home" , "Person forced from country" .)