From Longman Dictionary of Contemporary Englishcarelesscare‧less /ˈkeələs $ ˈker-/ ●●○ adjective1CARELESSnot paying enough attention to what you are doing, so that you make mistakes, damage things etc opp carefulIt was careless of him to leave the door unlocked.a careless mistakecareless drivingcareless withHe’s careless with his glasses and has lost three pairs.Careless talk can be disastrous for a business.2PLAN[usually before noun]natural and not done with any deliberateeffort or attentionHe ran a hand through his hair with a careless gesture.3IGNOREnot concerned about somethingcareless ofa man careless of his own safetyShe gave a careless shrug. ► Do not use ‘careless’ to mean that someone has no worries. Use carefree: They all felt happy and carefree. —carelessly adverb —carelessness noun [uncountable]THESAURUScareless not paying enough attention to what you are doing, so that you make mistakes, damage things etcI made a few careless mistakes.It was careless of you to leave your purse lying about.He started getting careless about taking his medication.clumsy often dropping or breaking things because you move around in a careless wayI’m so clumsy, I spilt milk all over the floor.a clumsy childsloppy careless and lazy in the way you do your work or in your behaviour generallyAs a student, he was brilliant but sloppy.I will not tolerate sloppy work.reckless especially written doing dangerous or stupid things without thinking about your own or other people’s safetyThe driver of the car was arrested for reckless driving.His actions showed a reckless disregard for human life.irresponsible careless in a way that might affect other people, especially when you should be taking care of themIt’s irresponsible for parents to let their children smoke.his irresponsible attitude to keeping animalstactless carelessly saying something that upsets or embarrasses someone, without intending to do thisHe kept making tactless remarks about her appearance. a tactless questionI thought it would be tactless to ask about her divorce.casual not being careful enough about something and treating it as though it is not importantHe seems to have a very casual attitude towards his work.She disliked the casual way in which he made decisions affecting other people’s lives. negligent careless about something that you are responsible for, so that serious mistakes are made – used especially when someone will be officially punished for thisThe doctor was negligent in using the wrong type of needle.They found him guilty of negligent conduct.