Togetherness (6)
I believe the answer is:
unison
'togetherness' is the definition.
(being united or together)
This is the entire clue.
(Other definitions for unison that I've seen before include "Total agreement or concord" , "with regard to the pitch" , "All singing the same notes" , "Harmony - public services' trade union" , "All singing the same note" .)