ataraxia vs tranquillity

ataraxia and tranquillity both are nouns.

Word	Noun	Adjective	Verb	Adverb
ataraxia	Yes	No	No	No
tranquillity	Yes	No	No	No

As nouns, tranquillity is a hypernym of ataraxia; that is, tranquillity is a word with a broader meaning than ataraxia:

Other hypernyms of ataraxia include placidity, quiet, repose, serenity, tranquility.

ataraxia (noun)	tranquillity (noun)
peace of mind	a disposition free from stress or emotion
	a state of peace and quiet
	an untroubled state; free from disturbances