Thought"less*ness

Thoughtless \Thought"less\, adv.
   1. Lacking thought; careless; inconsiderate; rash; as, a
      thoughtless person, or act.
      [1913 Webster]

   2. Giddy; gay; dissipated. [R.] --Johnson.
      [1913 Webster]

   3. Deficient in reasoning power; stupid; dull.
      [1913 Webster]

            Thoughtless as monarch oaks that shade the plain.
                                                  --Dryden.
      [1913 Webster] -- {Thought"less*ly}, adv. --
      {Thought"less*ness}, n.
      [1913 Webster]
    

166 Moby Thesaurus words for "thoughtlessness":
      abandon, absentmindedness, asininity, battiness, brainlessness,
      buffoonery, callowness, caprice, careless abandon, carelessness,
      casualness, childishness, clownishness, crackpottedness,
      crankiness, craziness, cursoriness, daffiness, desipience,
      disregard, disregardfulness, distraction, easiness, eccentricity,
      empty-headedness, fatuity, fatuousness, fecklessness, flightiness,
      flippancy, folly, foolery, foolheadedness, foolishness,
      forgetfulness, frivolity, frivolousness, giddiness, goofiness,
      hastiness, heedlessness, idiocy, imbecility, immaturity,
      improvidence, imprudence, inability, inadeptness, inadequacy,
      inadvertence, inadvertency, inadvisability, inanity, inaptitude,
      inaptness, inattention, inattentiveness, incapability, incapacity,
      incompetence, incompetency, inconsiderateness, inconsideration,
      incuriosity, indexterity, indifference, indiscreetness,
      indiscretion, ineffectiveness, ineffectuality, inefficiency,
      ineptitude, ineptness, inexpedience, injudiciousness, inobservance,
      insanity, insouciance, irrationality, lack of foresight,
      lax stewardship, laziness, levity, lightmindedness, lunacy,
      madness, maladjustment, maladroitness, mediocrity, mercuriality,
      mindlessness, negligence, niaiserie, nonobservance, nugacity,
      nuttiness, oblivion, obliviousness, offhandedness, pedestrianism,
      perfunctoriness, pompousness, poor husbandry, puerility, queerness,
      reasonlessness, recklessness, regardlessness, rustiness, sappiness,
      screwiness, senselessness, shallowness, shiftlessness, silliness,
      skill-lessness, sprezzatura, stuffiness, stupidity, superficiality,
      tactlessness, thriftlessness, triflingness, triviality,
      unaccommodatingness, unalertness, unaptness, unawareness,
      uncleverness, unconsciousness, undeftness, undexterousness,
      undextrousness, unfitness, unfittedness, unheedfulness,
      unhelpfulness, unintelligence, unintentiveness, unmindfulness,
      unobligingness, unobservance, unpreparedness, unproficiency,
      unreadiness, unreason, unreasonableness, unschooledness,
      unsensibleness, unskillfulness, unsolicitousness, unsolicitude,
      unsoundness, unthinkingness, unthoughtfulness, untrainedness,
      unwariness, unwatchfulness, unwisdom, unwiseness, volatility,
      wackiness, weirdness, witlessness, zaniness, zanyism