Don single flower back-to-front, Brazilian style (5,4)
I believe the answer is:
bossa nova
'brazilian style' is the definition.
'don single flower back-to-front' is the wordplay.
'don' becomes 'boss'.
'single' becomes 'a'.
'flower' becomes 'avon' (River Avon - something which flows**).
'back-to-front' shows that the letters should be reversed in order.
'avon' written backwards gives 'nova'.
'boss'+'a'+'nova'='BOSSA NOVA'
(Other definitions for bossa nova that I've seen before include "lively dance" , "Brazilian music, rhythmically related to the samba" , "(Music for) a Brazilian dance" , "Dance from Brazil similar to samba" , "Brazil's measure" .)