It's admitted by twirling aristocrat with a bow (4)
I believe the answer is:
arco
'a bow' is the definition.
(I've seen this before)
'it's admitted by twirling aristocrat with' is the wordplay.
'twirling' says the letters should be written in reverse.
'it's admitted by' indicates a hidden word.
'ocra' is hidden in the letters of 'aristocrat with'.
'ocra' reversed gives 'ARCO'.
(Other definitions for arco that I've seen before include "which every violinist must grasp" , "Musical direction" , "Played with the bow" , "taking a bow" , "bow for players" .)