impassivity vs impassiveness

impassivity and impassiveness both are nouns.

Word	Noun	Adjective	Verb	Adverb
impassivity	Yes	No	No	No
impassiveness	Yes	No	No	No

As nouns, impassivity and impassiveness are synonyms defined as:

impassivity and impassiveness: apathy demonstrated by an absence of emotional reactions

Other synonyms of impassivity include emotionlessness, indifference, phlegm, stolidity, unemotionality.

impassivity (noun)	impassiveness (noun)
apathy demonstrated by an absence of emotional reactions	apathy demonstrated by an absence of emotional reactions