DISASTROUS
black, calamitous, disastrous, fatal, fateful
(adjective) (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”
Source: WordNet® 3.1
Etymology
Adjective
disastrous (comparative more disastrous, superlative most disastrous)
Of the nature of a disaster; calamitous.
Foreboding disaster; ill-omened.
Synonyms
• (calamitous): cataclysmic, catastrophic
• (ill-omened): ill-boding, inauspicious, sinister
Antonyms
• auspicious
• fortunate
Source: Wiktionary
Dis*as"trous, a. Etym: [Cf. F. désastreux. See Disaster.]
1. Full of unpropitious stellar influences; unpropitious; ill-boding.
[Obs.]
The moon In dim eclipse, disastrous twilight sheds. Milton.
2. Attended with suffering or disaster; very unfortunate; calamitous;
ill-fated; as, a disastrous day; a disastrous termination of an
undertaking.
Wherein I spake of most disastrous chances. Shak.
– Dis*as"trous*ly, adv.
– Dis*as"trous*ness, n.
Source: Webster’s Unabridged Dictionary 1913 Edition