Calm in partnership (8)
I believe the answer is:
together
I believe this clue is a double definition.
'calm' is the first definition.
(thesaurus)
'in partnership' is the second definition.
(thesaurus)
(Other definitions for together that I've seen before include "In unison" , "Well-controlled" , "In conjunction, combined" , "as a group" , "stable" .)