regardless vs careless

regardless and careless both are adjectives.

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

As adjectives, regardless and careless are synonyms defined as:

regardless and careless: (usually followed by `of') without due thought or consideration

regardless (adjective)	careless (adjective)
(usually followed by `of') without due thought or consideration	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

regardless (adverb)	careless (adverb)
in spite of everything; without regard to drawbacks