[1] : The Collaborative International Dictionary of English v.0.48

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"lessly, adv. --
      thought"lessness, n.
      1913 webster
see also:
thought"lessly thought"lessness 

[2] : WordNet (r) 2.0

thoughtless
     adj 1: showing lack of careful thought; "the debate turned into
            thoughtless bickering" ant: thoughtful
     2: marked by or paying little heed or attention; "we have
        always known that heedless self-interest was bad morals;
        we know now that it is bad economics"--franklin d.
        roosevelt; "heedless of danger"; "heedless of the child's
        crying" syn: heedless, unheeding ant: heedful
     3: without care or thought for others; "the thoughtless saying
        of a great princess on being informed that the people had
        no bread; `let them eat cake'" syn: uncaring, unthinking
     4: 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: carelessp,
         thoughtlessp, regardless
see also:
thoughtful heedless unheeding heedful uncaring unthinking 
carelessp thoughtlessp regardless 

[3] : Moby Thesaurus II by Grady Ward, 1.0

217 moby thesaurus words for "thoughtless":
   absent-minded, airy, apish, arbitrary, artless, asinine, batty,
   befooled, beguiled, besotted, blank, blankminded, brainless, brash,
   buffoonish, calm, capricious, careless, casual, cockeyed, crazy,
   credulous, cursory, daffy, daft, dazed, degage, discourteous,
   disregardant, disregardful, distracted, distrait, dizzy, doting,
   dumb, easygoing, empty, empty-headed, fatuitous, fatuous,
   featherbrained, featherheaded, feckless, flaky, flippant, fluttery,
   fond, fool, foolheaded, foolish, forgetful, free and easy,
   frivolous, fuddled, futile, gaga, giddy, giddy-brained,
   giddy-headed, giddy-pated, giddy-witted, goofy, grasshopper,
   gulled, half-assed, happy-go-lucky, harebrain, harebrained, hasty,
   heedless, hotheaded, idiotic, ill-advised, ill-considered,
   ill-contrived, ill-devised, ill-gauged, ill-judged, imbecile,
   impolite, impolitic, improvident, imprudent, inadept, inadvertent,
   inadvisable, inane, inapt, inattentive, incautious, incogitant,
   inconsiderate, incurious, indifferent, indiscreet, inefficient,
   inept, inexpedient, inexpert, infatuated, injudicious, inobservant,
   insane, insensate, insensitive, insouciant, irrational, kooky,
   lazy, loony, mad, madcap, maudlin, mediocre, mindless, misadvised,
   misguided, moronic, myopic, neglectful, negligent, nirvanic, nutty,
   oblivious, offhand, passive, pedestrian, perfunctory, poor,
   quietistic, rash, rattlebrained, rattleheaded, rattlepated,
   reasonless, reckless, regardless, relaxed, remiss, respectless,
   rude, sappy, scatterbrained, scramblebrained, screwy, selfish,
   senseless, sentimental, sharp, shatterbrained, shiftless,
   shortsighted, silly, skill-less, stupid, tactless, thoughtfree,
   thriftless, tranquil, unaccommodating, unadvised, unapt,
   uncalculating, uncaring, unceremonious, uncomplaisant,
   unconsidered, uncooperative, undeft, undexterous, undextrous,
   undiplomatic, undiscerning, uneconomical, unfacile, unforeseeing,
   ungracious, unguarded, unheedful, unheeding, unhelpful, unideaed,
   unintellectual, unintelligent, unmarking, unmindful, unnoticing,
   unnoting, unobliging, unobservant, unobserving, unoccupied,
   unprepared, unproficient, unproviding, unready, unreasonable,
   unreasoning, unreflecting, unreflective, unremarking, unseeing,
   unsensible, unskillful, unsolicitous, unsound, untactful,
   unthinking, unthoughtful, unthrifty, unwise, vacant, vacuous,
   wacky, wet, witless, wrecking

Thoughtless >> T Words
Thoughtless, definition of term: Thoughtless
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