tranquility vs serenity

tranquility and serenity both are nouns.

Word	Noun	Adjective	Verb	Adverb
tranquility	Yes	No	No	No
serenity	Yes	No	No	No

As nouns, tranquility and serenity are synonyms defined as:

Other synonyms of tranquility include placidity, quiet, repose, tranquillity.

As nouns, serenity is a hyponym of tranquility; that is, serenity is a word with a more specific, narrower meaning than tranquility:

Other hyponyms of tranquility include ataraxis, heartsease, peace, peace of mind, peacefulness, repose, easiness, relaxation.

tranquility (noun)	serenity (noun)
a disposition free from stress or emotion	a disposition free from stress or emotion
a state of peace and quiet	the absence of mental stress or anxiety
an untroubled state; free from disturbances