serenity

Short definition from Wiktionary

Noun

1. 1
   The state of being serene; calmness; peacefulness.
2. 2
   A lack of agitation or disturbance.
3. 3
   A title given to a reigning prince or similar dignitary.

Proper noun

1. 1
   A female given name from English in general use since the 1990s.