The Collaborative International Dictionary of English v.0.48:

Fateful \Fate"ful\, a. .
   Having the power of serving or accomplishing fate. "The
   fateful steel." --J. Barlow.
   [1913 Webster]

   2. Significant of fate; ominous.
      [1913 Webster]

            The fateful cawings of the crow.      --Longfellow.
      -- Fate"ful*ly, adv.- Fate"ful*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fateful
    adj 1: having momentous consequences; of decisive importance;
           "that fateful meeting of the U.N. when...it declared war
           on North Korea"- Saturday Rev; "the fatal day of the
           election finally arrived" [syn: fateful, fatal]
    2: ominously prophetic [syn: fateful, foreboding(a),
       portentous]
    3: (of events) having extremely unfortunate or dire
       consequences; bringing ruin; "the stock market crashed on
       Black Friday"; "a calamitous defeat"; "the battle was a
       disastrous end to a disastrous campaign"; "such doctrines, if
       true, would be absolutely fatal to my theory"- Charles
       Darwin; "it is fatal to enter any war without the will to win
       it"- Douglas MacArthur; "a fateful error" [syn: black,
       calamitous, disastrous, fatal, fateful]
    4: controlled or decreed by fate; predetermined; "a fatal series
       of events" [syn: fatal, fateful]

Moby Thesaurus II by Grady Ward, 1.0:

126 Moby Thesaurus words for "fateful":
   acute, apocalyptic, appointed, awe-inspiring, bad, baleful,
   baneful, black, bodeful, boding, calamitous, cataclysmal,
   cataclysmic, catastrophic, certain, conclusive, consequential,
   consuming, consumptive, critical, crucial, dark, deadly, decisive,
   demolishing, demolitionary, depredatory, desolating, destined,
   destroying, destructive, determinative, devastating, devoted, dire,
   direful, disastrous, doomed, doomful, dreary, earnest, evil,
   evil-starred, fatal, fated, foreboding, foredoomed, formidable,
   fratricidal, gloomy, grave, heavy, ill, ill-boding, ill-fated,
   ill-omened, ill-starred, important, imposing, in store,
   in the cards, inauspicious, indefeasible, ineluctable, inescapable,
   inevasible, inevitable, inexorable, inflexible, internecine,
   irresistible, irrevocable, lethal, lowering, major, marked,
   menacing, momentous, necessary, nihilist, nihilistic,
   of evil portent, ominous, ordained, pivotal, portending,
   portentous, ravaging, relentless, resistless, ruining, ruinous,
   self-destructive, serious, significant, sinister, sober, solemn,
   somber, subversionary, subversive, suicidal, sure, sure as death,
   sure as fate, threatening, unavoidable, uncontrollable,
   undeflectable, unfavorable, unfortunate, unlucky, unpreventable,
   unpromising, unpropitious, unstoppable, untoward, unyielding,
   vandalic, vandalish, vandalistic, wasteful, wasting, weighty,
   withering, written