The Collaborative International Dictionary of English v.0.48:

Inconsiderate \In`con*sid"er*ate\, a. [L. inconsideratus. See
   In- not, and Considerate.]
   [1913 Webster]
   1. Not considerate; not attentive to safety or to propriety;
      not regarding the rights or feelings of others; hasty;
      careless; thoughtless; heedless; as, the young are
      generally inconsiderate; inconsiderate conduct.
      [1913 Webster]

            It is a very unhappy token of our corruption, that
            there should be any so inconsiderate among us as to
            sacrifice morality to politics.       --Addison.
      [1913 Webster]

   2. Inconsiderable. [Obs.] --E. Terry.

   Syn: Thoughtless; inattentive; inadvertent; heedless;
        negligent; improvident; careless; imprudent; indiscreet;
        incautious; injudicious; rash; hasty.
        [1913 Webster]

WordNet (r) 3.0 (2006):

inconsiderate
    adj 1: lacking regard for the rights or feelings of others;
           "shockingly inconsiderate behavior" [ant: considerate]
    2: without proper consideration or reflection; "slovenly
       inconsiderate reasoning"; "unconsidered words"; "prejudice is
       the holding of unconsidered opinions" [syn: inconsiderate,
       unconsidered]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "inconsiderate":
   airy, arbitrary, boorish, brash, caddish, capricious, careless,
   casual, coarse, crude, cursory, degage, disregardant, disregardful,
   easygoing, flippant, forgetful, free and easy, hasty, heedless,
   hotheaded, ill-advised, ill-bred, ill-considered, ill-contrived,
   ill-devised, ill-gauged, ill-judged, impolitic, imprudent,
   inadvertent, inadvisable, incautious, indifferent, indiscreet,
   inexpedient, injudicious, insensate, insensitive, insouciant,
   intolerant, irrational, lazy, loutish, louty, madcap, mindless,
   misadvised, misguided, myopic, nasty, oblivious, offensive,
   offhand, perfunctory, rash, reasonless, reckless, regardless,
   respectless, rude, senseless, sharp, shortsighted, tactless,
   thoughtless, unaccommodating, unadvised, uncalculating, uncaring,
   unceremonious, uncomplaisant, unconcerned, unconsidered,
   uncooperative, undiplomatic, undiscerning, unfeminine,
   unforeseeing, ungenteel, ungentle, ungentlemanly, ungracious,
   unguarded, unheedful, unheeding, unhelpful, unladylike, unmindful,
   unobliging, unprepared, unready, unreasonable, unreasoning,
   unrefined, unreflecting, unreflective, unseeing, unsensible,
   unsolicitous, unsound, unsympathetic, untactful, unthinking,
   unthoughtful, unwise, vulgar, witless