Titled person on revolving bar (7)
I believe the answer is:
counter
'bar' is the definition.
(I've seen this in other clues)
'titled person on revolving' is the wordplay.
'titled person' becomes 'count'.
'on' becomes 're' ('on' can be mean 'with reference to').
'revolving' says the letters should be written backwards.
're' in reverse letter order is 'er'.
'count'+'er'='COUNTER'
(Other definitions for counter that I've seen before include "Piece in board game" , "Retaliate" , "Where to pay in shop" , "It's quite the opposite" , "Parry" .)