Calmness: - 

“By staying calm, you increase your resistance against any kind of storms.” ― Mehmet Murat ildan

Inner peace :- 

“The life of inner peace, being harmonious and without stress, is the easiest type of existence.”

Peacefulness:- 

“There can be no world peace without inner peace.” ― A.J. Garce

Tranquillity: -

“Only the development of compassion and understanding for others can bring us the tranquility and happiness we all seek.” ― Dalai Lama XIV

Equanimity: - 

“A modern definition of equanimity: cool. This refers to one whose mind remains stable & calm in all situations.”

Composure: - 

"The soldier must be calm in the thick of the battle," pursued the policeman. "The composure of an army is the anger of a nation.” ― G.K. Chesterton.

Repose: - 

You must learn to be still in the midst of activity and to be vibrantly alive in repose.

Restfulness:-   

Sometimes the most important thing in a whole day is the rest we take between two deep breaths, or the turning inwards in prayer for five short minutes.- Etty Hillesum

Serenity:- 

Every breath we take, every step we make, can be filled with peace, joy and serenity.

Stillness :-  

Stillness is a calm, quiet, motionless state. As you look out at the lake, the stillness of the water is a sign that you should take out the canoe rather than the sailboat.