ataraxia vs placidity

ataraxia and placidity both are nouns.

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

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

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

ataraxia (noun)	placidity (noun)
peace of mind	a disposition free from stress or emotion
	a feeling of calmness; a quiet and undisturbed feeling