Calm surrounds every other part of unitary authority (7)
I believe the answer is:
control
'calm' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for control that I've seen before include "Keep in line" , "Mastery" , "Power to restrain or regulate" , "domination" , "Authority" .)