The Collaborative International Dictionary of English v.0.48:

Unconsidered \Un`con*sid"ered\, a.
   Not considered or attended to; not regarded; inconsiderable;
   trifling.
   [1913 Webster]

         A snapper-up of unconsidered trifles.    --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unconsidered
    adj 1: 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:

132 Moby Thesaurus words for "unconsidered":
   abandoned, aimless, automatic, brash, casual, deserted, designless,
   desultory, disregarded, gut, half-done, haphazard, hasty,
   hit-or-miss, hotheaded, ignored, ill-advised, ill-considered,
   ill-contrived, ill-devised, ill-gauged, ill-judged, imageless,
   impolitic, imprudent, inadvertent, inadvisable, incautious,
   inconsequent, inconsequential, inconsiderable, inconsiderate,
   indeliberate, indiscreet, indiscriminate, inexpedient, injudicious,
   insensate, involuntary, irrational, laid aside, left undone,
   mindless, misadvised, misguided, missed, myopic, neglected,
   omitted, overlooked, paltry, passed by, passed over, passed up,
   picayune, pigeonholed, promiscuous, puny, put aside, reasonless,
   reckless, reflex, reflexive, senseless, shortsighted, shunted,
   sidelined, sidetracked, slighted, small, snap, spontaneous,
   thoughtless, trifling, trivial, unadvised, unasked, unattended to,
   uncalculated, uncared-for, unchaperoned, unconceived,
   unconceptualized, unconscious, undeliberate, undeliberated,
   undescried, undesigned, undiscerning, undone, undreamed-of,
   unexamined, unexplored, unforeseeing, unheeded, unimaged,
   unimagined, unintended, unintentional, unmarked, unmeditated,
   unminded, unmissed, unnoted, unnoticed, unobserved, unperceived,
   unplanned, unpremeditated, unreasonable, unreflecting,
   unreflective, unregarded, unremarked, unscanned, unsearched,
   unseeing, unseen, unsensible, unsifted, unsolicited, unsound,
   unstudied, untended, unthinking, unthought-of, unthoughtful,
   unwatched, unweighed, unwilled, unwise, witless