Song's good within musical (8)
I believe the answer is:
carousel
'musical' is the definition.
(I've seen this before)
'song's good within' is the wordplay.
'song' becomes 'carol' (carol is a kind of song**).
'good' becomes 'use' (in phrases like 'it's no good', 'any good?' etc).
'within' indicates putting letters inside.
'carol' placed around 'use' is 'CAROUSEL'.
(Other definitions for carousel that I've seen before include "fairground entertainment" , "it's located in 'Arrivals'" , "Does Carol use this piece of fairground equipment?" , "fair entertainment?" , "A closure (anag.)" .)