Harmony, accord (5)
I believe the answer is:
unity
This clue is a double definition.
'harmony' is the first definition.
(I've seen this in another clue)
'accord' is the second definition.
(I've seen this in another clue)
(Other definitions for unity that I've seen before include "Mitford girl" , "State of togetherness" , "One - mutual agreement" , "Accord" , "State of complete and harmonious whole" .)