In feudal society as well (4)
I believe the answer is:
also
'as well' is the definition.
(synonyms)
'in feudal society' is the wordplay.
'in' says the answer is hidden in the clue.
'ALSO' is hidden within 'feudal society'.
(Other definitions for also that I've seen before include "Item" , "in accompaniment" , "on top" , "To boot" , "Old" .)