Discipline citizen (7)
I believe the answer is:
subject
This clue is a double definition.
'discipline' is the first definition.
('subject' can be a synonym of 'discipline')
'citizen' is the second definition.
(I've seen this before)
(Other definitions for subject that I've seen before include "Theme, topic" , "Division of curriculum" , "Topic being discussed" , "What ruler is not" , "Branch of knowledge" .)