Reaches note in popular song. That's expedient (9)
I believe the answer is:
makeshift
'expedient' is the definition.
(I know that makeshift is a type of expedient)
'reaches note in popular song' is the wordplay.
'reaches' becomes 'makes' ('make' can be a synonym of 'reach').
'note' becomes 'f' (musical note).
'in' is an insertion indicator.
'popular song' becomes 'hit' (a hit song).
'f' put within 'hit' is 'hift'.
'makes'+'hift'='MAKESHIFT'
'that's' is the link.
(Other definitions for makeshift that I've seen before include "Cobbled together" , "serving temporarily?" , "What 11 [SEAMSTRESS] might do" , "temporary expedient" , "Rough-and-ready" .)