1. [adjective] (archaic) Free from care; unworried, without anxiety. [from 11thc.]
2. [adjective] Not concerned or worried (about). [from 11thc.]
3. [adjective] Not giving sufficient attention or thought, especially concerning the avoidance of harm or mistakes. [from 16thc.]
4. [adjective] 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'.
5. [adjective] Effortless and unstudied; 'an impression of careless elegance'; 'danced with careless grace'.
6. [adjective] (usually followed by `of') without due thought or consideration; 'careless of the consequences'; 'crushing the blooms with regardless tread'.