Musical, musical bunch! (9)
I believe the answer is:
hairspray
'musical' is the definition.
(US musical)
'musical bunch' is the wordplay.
'musical' becomes 'hair' (1960s musical).
'bunch' becomes 'spray' (I have seen 'Bunch of flowers' mean 'spray' so perhaps 'bunch' could also mean 'spray').
'hair'+'spray'='HAIRSPRAY'
(Other definitions for hairspray that I've seen before include "fine solution" , "setter" , "pressurised stuff?" , "Barnet manager" .)