Advantage admitted by landed gentry (4)
I believe the answer is:
edge
'advantage' is the definition.
(I've seen this before)
'admitted by landed gentry' is the wordplay.
'admitted by' indicates a hidden word.
'EDGE' is hidden within 'landed gentry'.
(Other definitions for edge that I've seen before include "Verge" , "Bind" , "Border, fringe" , "Line where soething begins or ends" , "Periphery" .)