From The Collaborative International Dictionary of English v.0.48 [gcide]:
Disastrous \Dis*as"trous\, a. [Cf. F. d['e]sastreux. See
Disaster.]
1. Full of unpropitious stellar influences; unpropitious;
ill-boding. [Obs.]
[1913 Webster]
The moon
In dim eclipse, disastrous twilight sheds. --Milton.
[1913 Webster]
2. Attended with suffering or disaster; very unfortunate;
calamitous; ill-fated; ending in utter failure or ruin;
as, a disastrous day; a disastrous termination of an
undertaking.
[1913 Webster]
Wherein I spake of most disastrous chances. --Shak.
-- Dis*as"trous*ly, adv. -- Dis*as"trous*ness, n.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
disastrous
adj 1: (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]