Source : Webster's Revised Unabridged Dictionary (1913)

Careless \Care"less\, a. [AS. cearle['a]s.]
   1. Free from care or anxiety. hence, cheerful; light-hearted.
      --Spenser.

            Sleep she as sound as careless infancy. --Shak.

   2. Having no care; not taking ordinary or proper care;
      negligent; unconcerned; heedless; inattentive; unmindful;
      regardless.

            My brother was too careless of his charge. --Shak.

            He grew careless of himself.          --Steele.

   3. Without thought or purpose; without due care; without
      attention to rule or system; unstudied; inconsiderate;
      spontaneous; rash; as, a careless throw; a careless
      expression.

            He framed the careless rhyme.         --Beattie.

   4. Not receiving care; uncared for. [R.]

            Their many wounds and careless harms. --Spenser.

   Syn: Negligent; heedless; thoughtless; unthinking;
        inattentive; incautious; remiss; supine; forgetful;
        regardless; inconsiderate; listless.

Source : WordNet®

careless
     adj 1: 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"
            [ant: {careful}]
     2: effortless and unstudied; "an impression of careless
        elegance"; "danced with careless grace"
     3: (usually followed by `of') without due thought or
        consideration; "careless of the consequences"; "the
        proverbial grasshopper--thoughtless of tomorrow";
        "crushing the blooms with regardless tread" [syn: {careless(p)},
         {thoughtless(p)}, {regardless}]
     4: showing an unthinking lack of consideration; "a careless
        remark"