Excellent being on leave in a NE region of France (9)
I believe the answer is:
aquitaine
'region of france' is the definition.
(I've seen this before)
'excellent being on leave in a ne' is the wordplay.
'excellent' becomes 'ai' (resembles 'Aq', old-fashioned term for excellent).
'being on' means one lot of letters go next to another.
'leave' becomes 'quit' (quitting is a kind of leaving).
'in' is an insertion indicator.
'ai' after 'quit' is 'quitai'.
'a'+'ne'='ane'
'quitai' inserted into 'ane' is 'AQUITAINE'.
(Other definitions for aquitaine that I've seen before include "historical region of France" , "Region in SW France" , "Formerly English region of France" , "somewhere in France" , "French region" .)