National topic (7)
I believe the answer is:
subject
I believe this clue is a double definition.
'national' is the first definition.
('subject' can be a synonym of 'national')
'topic' is the second definition.
('subject' can be a synonym of 'topic')
(Other definitions for subject that I've seen before include "A national - topic of discussion" , "Person under 26?" , "School topic" , "Theme, topic" , "Theme (of a fugue)" .)