Insert in ballad (5)
I believe the answer is:
inlay
'insert' is the definition.
(thesaurus)
'in ballad' is the wordplay.
'ballad' becomes 'lay' ('lay' can be a synonym of 'ballad').
'in'+'lay'='INLAY'
(Other definitions for inlay that I've seen before include "Insert wood, stone or metal into a surface" , "Decorate by embedding" , "Mix images" , "Filling shaped to fit a tooth cavity" , "Decoration of a surface by inserting wood, stone or metal" .)