1. (adv.) Lacking thought; careless; inconsiderate; rash; as, a thoughtless person, or act.

2. (adv.) Giddy; gay; dissipated.

3. (adv.) Deficient in reasoning power; stupid; dull.

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