thoughtlessness vs inconsiderateness

thoughtlessness and inconsiderateness both are nouns.

Word	Noun	Adjective	Verb	Adverb
thoughtlessness	Yes	No	No	No
inconsiderateness	Yes	No	No	No

As nouns, thoughtlessness and inconsiderateness are synonyms defined as:

thoughtlessness and inconsiderateness: the quality of failing to be considerate of others

Other synonyms of thoughtlessness include inconsideration.

thoughtlessness (noun)	inconsiderateness (noun)
the trait of not thinking carefully before acting	the quality of failing to be considerate of others
the quality of failing to be considerate of others