Musical number with good numbers making a comeback ... (4)
I believe the answer is:
Here is my best explanation:
'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 "Piece of music, usually with words", "Musical rendition", "Ballad, aria", "Air", "Musical number", "Music with words", "Tune", "Vocal composition", "Vocal music" and "Musical composition with words".)