emotionlessness vs impassiveness

emotionlessness and impassiveness both are nouns.

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

As nouns, emotionlessness and impassiveness are synonyms defined as:

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

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

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