Insert fashionable song (5)
I believe the answer is:
inlay
'insert' is the definition.
(thesaurus)
'fashionable song' is the wordplay.
'fashionable' becomes 'in' ('in' can be similar in meaning to 'fashionable').
'song' becomes 'lay' (lay is a kind of song).
'in'+'lay'='INLAY'
(Other definitions for inlay that I've seen before include "Type of woodwork" , "Decorate by embedding" , "Inserted decoration" , "Insert wood, stone or metal into a surface" , "Embed" .)