Completely calm (6)
I believe the answer is:
serene
'completely calm' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for serene that I've seen before include "Calm and at peace" , "Peaceful and contented" , "Peaceful and unruffled" , "Tranquil, unruffled" , "Not agitated" .)