placidity vs equanimity

placidity and equanimity both are nouns.

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

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

Other hypernyms of placidity include calm, calmness, composure.

placidity (noun)	equanimity (noun)
a disposition free from stress or emotion	steadiness of mind under stress
a feeling of calmness; a quiet and undisturbed feeling