The Collaborative International Dictionary of English v.0.48:

Fatal \Fa"tal\, a. [L. fatalis, fr. fatum: cf. F. fatal. See
   Fate.]
   1. Proceeding from, or appointed by, fate or destiny;
      necessary; inevitable. [R.]
      [1913 Webster]

            These thing are fatal and necessary.  --Tillotson.
      [1913 Webster]

            It was fatal to the king to fight for his money.
                                                  --Bacon.
      [1913 Webster]

   2. Foreboding death or great disaster. [R.]
      [1913 Webster]

            That fatal screech owl to our house
            That nothing sung but death to us and ours. --Shak.
      [1913 Webster]

   3. Causing death or destruction; deadly; mortal; destructive;
      calamitous; as, a fatal wound; a fatal disease; a fatal
      day; a fatal error.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fatal
    adj 1: bringing death [ant: nonfatal]
    2: 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]
    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:

187 Moby Thesaurus words for "fatal":
   accidental, adventitious, aleatory, appointed, approaching,
   awe-inspiring, badly off, baleful, baneful, black, brutal,
   calamitous, casual, casualty, cataclysmal, cataclysmic,
   catastrophic, causeless, chance, chancy, coming, consuming,
   consumptive, contingent, damaging, deadliness, deadly, death,
   death-bringing, deathful, deathly, decreed, demolishing,
   demolitionary, depredatory, depressed, desired, desolating,
   destinal, destined, destroying, destructive, determined,
   devastating, devoted, dicey, dire, disastrous, donsie, doomed,
   doomful, dreadful, earnest, emergent, essential, eventual,
   evil-starred, extrapolated, fatality, fated, fateful, fatidic,
   feral, final, fluky, foredoomed, foreordained, formidable,
   forthcoming, fortuitous, fortuneless, fratricidal, funest, future,
   futuristic, grave, grievous, hapless, harmful, heavy, hereafter,
   hoped-for, iffy, ill off, ill-fated, ill-starred, imminent,
   imposing, in adverse circumstances, in store, in the cards,
   inauspicious, incidental, indeterminate, ineluctable, inescapable,
   inevitable, internecine, killing, later, lethal, lethality,
   luckless, malefic, maleficent, malign, malignancy, malignant,
   marked, mischievous, mortal, mortality, murderous, nearing,
   necessary, nihilist, nihilistic, noxiousness, ominous, ordained,
   out of luck, pernicious, perniciousness, pestilent, pestilential,
   planet-struck, planned, plotted, poisonous, poisonousness,
   portentous, predestined, predetermined, predicted, preordained,
   probable, projected, prophesied, prospective, ravaging, risky,
   ruining, ruinous, sad, savage, self-destructive, serious,
   short of luck, sinister, sober, solemn, star-crossed,
   subversionary, subversive, suicidal, terminal, to come, to-be,
   toxic, tragic, ultimate, unavoidable, unblessed, uncaused,
   underprivileged, undetermined, unexpected, unforeseeable,
   unforeseen, unfortunate, unhappy, unlooked-for, unlucky,
   unpredictable, unprosperous, unprovidential, vandalic, vandalish,
   vandalistic, virulence, virulent, wasteful, wasting, weighty,
   withering, wreckful, written



The Free On-line Dictionary of Computing (30 December 2018):

fatal

    Resulting in termination of the program.

   (1997-08-03)