Lord once kept in privilege illegally rejected (5)
I believe the answer is:
liege
'lord once' is the definition.
(feudal term for one's superior)
'kept in privilege illegally rejected' is the wordplay.
'kept in' indicates the answer is hidden within the clue.
'rejected' is a reversal indicator.
'egeil' is hidden within 'privilege illegally'.
'egeil' in reverse letter order is 'LIEGE'.
(Other definitions for liege that I've seen before include "Belgian city or ancient superior" , "Large Belgian city" , "European university" , "Vassal, subject" , "Faithful," .)