Tranquility
Part of speech: noun
Definition: The state of being tranquil
Example sentence: Movement is tranquility.
Tranquillity
Part of speech: noun
Definition: the state of being tranquilthe absence of disturbance; peacefulnessthe absence of stress; serenitythe quality of calm such as that experienced in places with mainly natural features and activities, free from disturbance from manmade ones.
Example sentence: Like ships that have gone down at sea, when heaven was all tranquillity.