A musical quality in harmony (5)
I believe the answer is:
music
I believe this is a double definition.
'a musical quality' is the first definition.
(I know this)
'harmony' is the second definition.
(I've seen this before)
'in' acts as a link.
(Other definitions for music that I've seen before include "Art (of noise)" , "Staff will support this" , "Sweet sound." , "Harmonious sound (generally!)" , "'My - - ' , radio quiz" .)