Brit maybe showing discipline (7)
I believe the answer is:
subject
'discipline' is the definition.
(synonyms)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for subject that I've seen before include "Theme - one under rule" , "UK citizen?" , "Theme, topic" , "Put down" , "Topic - branch of study - citizen" .)