hardheartedness vs heartlessness

hardheartedness and heartlessness both are nouns.

Word	Noun	Adjective	Verb	Adverb
hardheartedness	Yes	No	No	No
heartlessness	Yes	No	No	No

As nouns, hardheartedness and heartlessness are synonyms defined as:

hardheartedness and heartlessness: an absence of concern for the welfare of others

Other synonyms of hardheartedness include coldheartedness.

hardheartedness (noun)	heartlessness (noun)
an absence of concern for the welfare of others	an absence of concern for the welfare of others