Subservient to a French communist revolutionary (5)
I believe the answer is:
under
'subservient to' is the definition.
(as in working 'under' a supervisor or manager)
'a french communist revolutionary' is the wordplay.
'a french' becomes 'un' ('a' in French).
'communist' becomes 'red' (red can informally mean communist).
'revolutionary' says the letters should be written backwards.
'red' back-to-front is 'der'.
'un'+'der'='UNDER'
(Other definitions for under that I've seen before include "Governed by" , "See 16 Down" , "See 7" , "Managed by" , "Dylan Thomas radio play ''.... Milk Wood''" .)