careless vs regardless

careless and regardless both are adjectives.

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

As adjectives, careless and regardless are synonyms defined as:

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

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

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