Very good on a revolutionary instrument (5)
I believe the answer is:
piano
'instrument' is the definition.
(piano is a kind of instrument)
'very good on a revolutionary' is the wordplay.
'very good' becomes 'pi' (I've seen this in other clues**).
'revolutionary' shows that the letters should be reversed in order.
'on'+'a'='ona'
'ona' in reverse letter order is 'ano'.
'pi'+'ano'='PIANO'
(Other definitions for piano that I've seen before include "Keyboard instrument" , "In music, soflty" , "Soft - musical instrument" , "Franz Liszt's instrument" , "soft passage" .)