WordNet (r) 3.0 (2006):

ill-considered
    adj 1: not given careful consideration; "ill-considered actions
           often result in disaster"; "an ill-judged attempt" [syn:
           ill-considered, ill-judged, improvident,
           shortsighted]

Moby Thesaurus II by Grady Ward, 1.0:

141 Moby Thesaurus words for "ill-considered":
   a bit previous, advanced, automatic, bad, botched, bungled,
   butchered, casual, far ahead, forward, fumbled, futile, gut,
   half-baked, half-cocked, hasty, ill-advised, ill-contrived,
   ill-devised, ill-done, ill-executed, ill-gauged, ill-judged,
   ill-managed, ill-seasoned, ill-suited, ill-timed, impolitic,
   improper, imprudent, impulsive, inadvertent, inadvisable,
   inappropriate, inapt, inauspicious, incongruous, inconsiderate,
   inconvenient, indeliberate, indiscreet, inept, inexpedient,
   infelicitous, injudicious, inopportune, insensate, intempestive,
   intrusive, involuntary, irrational, irrelevant, late, mal a propos,
   malapropos, mindless, misadvised, misconducted, misdirected,
   misguided, mismanaged, mistimed, muffed, murdered, myopic,
   negligent, not firm, off base, out of line, out of phase,
   out of place, out of time, overhasty, oversoon, precipitate,
   precocious, premature, previous, reasonless, reckless, reflex,
   reflexive, rushed, senseless, shortsighted, snap, spoiled,
   spontaneous, thoughtless, too early, too late, too soon, unadvised,
   unbefitting, uncalculated, unconscious, unconsidered,
   uncrystallized, undeliberate, undeliberated, undesigned,
   undesirable, undiscerning, unfavorable, unfit, unfitting,
   unforeseeing, unfortunate, unhandy, unhappy, unintended,
   unintentional, unjelled, unlucky, unmatured, unmeditated, unmeet,
   unpremeditated, unprepared, unprofitable, unpropitious, unready,
   unreasonable, unreflecting, unreflective, unripe, unseasonable,
   unseeing, unseemly, unsensible, unsound, unstudied, unsuitable,
   unthinking, unthoughtful, untimely, untoward, unwilled, unwise,
   witless, wrong