Not concerned or worried (about). / Not giving sufficient attention or thought, especially concerning the avoidance of harm or mistakes. / (archaic) Free from care; unworried, without anxiety.

Lack of care; the state or quality of being careless.

plural of carelessness

Giving the appearance of carelessness; relaxedly. / Done without care or attention; inattentively.

superlative form of careless: most careless

Obsolete spelling of carelessness