impassiveness vs indifference

impassiveness and indifference both are nouns.

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

As nouns, impassiveness and indifference are synonyms defined as:

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

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

impassiveness (noun)	indifference (noun)
apathy demonstrated by an absence of emotional reactions	the trait of lacking enthusiasm for or interest in things generally
	the trait of remaining calm and seeming not to care; a casual lack of concern
	unbiased impartial unconcern
	apathy demonstrated by an absence of emotional reactions