Nationalist organised apt rebellion (7)
I believe the answer is:
patriot
'nationalist' is the definition.
('patriot' can be a synonym of 'nationalist')
'organised apt rebellion' is the wordplay.
'organised' indicates anagramming the letters.
'rebellion' becomes 'riot'.
'apt' is an anagram of 'pat'.
'pat'+'riot'='PATRIOT'
(Other definitions for patriot that I've seen before include "Country-lover" , "One who loves his or her country" , "No traitor" , "Country supporter" , "A lover of fatherland" .)