noun

failure to give sufficient attention to avoiding harm or errors; negligence.

most road accidents are caused by carelessness on the part of motorists

inattention,inattentiveness,heedlessness,thoughtlessness,negligence,improvidence,remissness,forgetfulness,absent-mindedness,irresponsibility,impetuosity,recklessness,rashness,laxity,laxness,slackness,clumsiness,ineptitude,oversight,omission,dereliction,sloppiness