1. careless (vs. careful), casual, cursory, passing(prenominal), perfunctory, haphazard, slapdash, slipshod, sloppy, heedless, reckless, incautious, offhand, offhanded, imprudent, inattentive, incautious, negligent, superficial, unconcerned

usage: marked by lack of attention or consideration or forethought or thoroughness; not careful; "careless about her clothes"; "forgotten by some careless person"; "a careless housekeeper"; "careless proofreading"; "it was a careless mistake"; "hurt by a careless remark"

2. careless, artless (vs. artful)

usage: effortless and unstudied; "an impression of careless elegance"; "danced with careless grace"

3. careless(predicate), regardless, heedless (vs. heedful), unheeding

usage: (usually followed by `of') without due thought or consideration; "careless of the consequences"; "crushing the blooms with regardless tread"

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See also: careless (Dictionary)