Tranquil silence, calmness (9)
I believe the answer is:
stillness
This clue is a double definition.
'tranquil silence' is the first definition.
(I've seen this before)
'calmness' is the second definition.
(I know that stillness is a type of calmness)
(Other definitions for stillness that I've seen before include "Quiet, calm" , "Motionlessness" , "Lack of movement" , "Immobility" , "Lack of activity" .)