thoughtlessness vs inconsideration

thoughtlessness and inconsideration both are nouns.

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

As nouns, thoughtlessness and inconsideration are synonyms defined as:

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

Other synonyms of thoughtlessness include inconsiderateness.

thoughtlessness (noun)	inconsideration (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