A little music with it, number for singer (8)
I believe the answer is:
baritone
'for singer' is the definition.
(baritone is a kind of singer)
'a little music with it number' is the wordplay.
'a little music' becomes 'bar' (a bar of music).
'with' means one lot of letters go next to another.
'number' becomes 'one' (one is a kind of whole number).
'bar'+'it'+'one'='BARITONE'
(Other definitions for baritone that I've seen before include "Second lowest male singing voice" , "Male singer between tenor and bass" , "solo voice" , "Male singer looks odd in boater" , "Male voice between bass and tenor" .)