Musical number with good numbers making a comeback ... (4)
I believe the answer is:
song
'musical number' is the definition.
(I've seen this before)
'with good numbers making a comeback' is the wordplay.
'with' says to put letters next to each other.
'good' becomes 'g' (abbreviation).
'numbers' becomes 'nos' (no. is a kind of number**).
'making a comeback' says the letters should be written backwards.
'g' put next to 'nos' is 'gnos'.
'gnos' in reverse letter order is 'SONG'.
(Other definitions for song that I've seen before include "Musical composition; air" , "Vocal composition" , "Melody (which is cheap to go for)" , "Something recorded by 26 [FACES] , for example" , "See 17" .)