carelessness vs careless

carelessness is a noun but careless is not a noun.

Word	Noun	Adjective	Verb	Adverb
carelessness	Yes	No	No	No
careless	No	Yes	No	No

carelessness (noun)	careless (noun)
failure to act with the prudence that a reasonable person would exercise under the same circumstances
the quality of not being careful or taking pains

carelessness (adjective)	careless (adjective)
	marked by lack of attention or consideration or forethought or thoroughness; not careful
	effortless and unstudied
	(usually followed by `of') without due thought or consideration