Subordinate going on about right cocktail (7)
I believe the answer is:
sidecar
'cocktail' is the definition.
(I know that sidecar is a type of cocktail)
'subordinate going on about right' is the wordplay.
'subordinate' becomes 'side' (side can mean subordinate or less important).
'going on' means one lot of letters go next to another.
'about' becomes 'ca' (short for circa).
'right' becomes 'r' (common abbreviation).
'side'+'ca'+'r'='SIDECAR'
(Other definitions for sidecar that I've seen before include "Cocktail; bike attachment" , "In which a passenger may be taken" , "that's suitable for a non-driver" , "Cocktail - cedar is (anag)" , "Motorbike passenger attachment" .)