Banish former partner on French island (5)
I believe the answer is:
exile
'banish' is the definition.
(I've seen this before)
'former partner on french island' is the wordplay.
'former partner' becomes 'ex'.
'on' means one lot of letters go next to another.
'french island' becomes 'ile' (French for 'island').
'ex'+'ile'='EXILE'
(Other definitions for exile that I've seen before include "officially banish" , "Person forced from country" , "One forced to live abroad" , "Person banished from the home country" , "Throw out" .)