Serenity etymology in English

English word serenity comes from Latin serenus

Dictionary entry	Language	Definition
serenus	Latin (lat)	(figuratively) Cheerful, glad, joyous.. Clear, fair, bright, serene, tranquil.. That clears the sky or brings fair weather.
serenitas	Latin (lat)	(figuratively) favourable conditions. Serenity; fine weather.
sérénité	Middle French (frm)
serenity	English (en)	A lack of agitation or disturbance.. A title given to a reigning prince or similar dignitary.. The state of being serene; calmness; peacefulness.

Serenity etymology