not paying enough attention to what one does

a careless typist.

not exact, accurate, or thorough

careless work.

done or said heedlessly or negligently; unconsidered

a careless remark.

not caring or troubling; having no care or concern; unconcerned (usually fol. by of, about, or in )

careless of the rights of others; careless about one's behavior; careless in speech.

possessed or caused without effort or art; unstudied

careless beauty.

Archaic . free from anxiety.

adverb

negligently , neglectfully , thoughtlessly , nonchalantly , offhandedly , rashly , hastily , inattentively , unmindfully , unconcernedly , incautiously , irresponsibly , without care , without concern , haphazardly , sloppily