Subordinate theme (7)
I believe the answer is:
subject
I believe this is a double definition.
'subordinate' is the first definition.
(similar in meaning)
'theme' is the second definition.
(synonyms)
(Other definitions for subject that I've seen before include "A national - topic of discussion" , "Topic - branch of study - citizen" , "Theme - one under rule" , "Citizenship' at school maybe" , "Theme (of a fugue)" .)