Calmness (5)
I believe the answer is:
peace
'calmness' is the definition.
(I know that peace is a type of quietness)
This is the entire clue.
(Other definitions for peace that I've seen before include "Calm, tranquility" , "Freedom from disturbance, tranquillity" , "Quiet companion" , "Calmness" , "still?" .)