Sound of harmony in musical composition (5)
I believe the answer is:
piece
'musical composition' is the definition.
(synonyms)
'sound of harmony' is the wordplay.
'sound of' shows a homophone (sound like).
'harmony' becomes 'peace' (both can mean cooperation or a lack of conflict).
'peace' sounds like 'PIECE'.
'in' is the link.
(Other definitions for piece that I've seen before include "Portion, bit" , "man on board" , "wedge a > bit" , "Musical work; bit" , "king or queen?" .)