The Collaborative International Dictionary of English v.0.48:

Heedless \Heed"less\, a.
   Without heed or care; inattentive; careless; thoughtless;
   unobservant.
   [1913 Webster]

         O, negligent and heedless discipline!    --Shak.
   [1913 Webster]

         The heedless lover does not know
         Whose eyes they are that wound him so.   --Waller.
   -- Heed"less*ly, adv. -- Heed"less*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

heedless
    adj 1: 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: attentive,
           heedful, paying attention, thoughtful]
    2: characterized by careless unconcern; "the heedless generosity
       and the spasmodic extravagance of persons used to large
       fortunes"- Edith Wharton; "reckless squandering of public
       funds" [syn: heedless, reckless]

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "heedless":
   Lethean, absentminded, airy, aloof, amnestic, apathetic, arbitrary,
   ataractic, blase, blind, blocked, bored, capricious, careless,
   casual, converted, cursory, deaf, degage, detached, devil-may-care,
   disinterested, dispassionate, disregardant, disregardful, distant,
   distracted, distrait, easygoing, feckless, flippant, forgetful,
   forgetting, free and easy, grasshopper, happy-go-lucky, impassive,
   improvident, inadvertent, inattentive, inclined to forget,
   inconsiderate, incurious, indifferent, inexcitable, inobservant,
   insouciant, lackadaisical, lazy, listless, mindless, neglectful,
   negligent, nonchalant, oblivious, offhand, perfunctory, phlegmatic,
   pococurante, reasonless, reckless, regardless, repressed,
   respectless, shiftless, stolid, suppressed, tactless, thoughtless,
   thriftless, turned-off, unaccommodating, unanxious, uncalculating,
   uncaring, uncomplaisant, unconcerned, uncooperative, undiplomatic,
   undiscriminating, uneconomical, unguarded, unheedful, unheeding,
   unhelpful, uninquiring, uninterested, uninvolved, unmarking,
   unmindful, unnoticing, unnoting, unobliging, unobservant,
   unobserving, unprepared, unproviding, unready, unreasoning,
   unreflecting, unreflective, unremarking, unsolicitous, untactful,
   unthinking, unthoughtful, unthrifty, withdrawn, wrecking