A disastrous event has extremely bad consequences and effects. the recent, disastrous earthquake = catastrophic + disastrously dis·as·trous·ly The vegetable harvest is disastrously behind schedule
(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"
Attended with suffering or disaster; very unfortunate; calamitous; ill-fated; as, a disastrous day; a disastrous termination of an undertaking
If you describe something as disastrous, you mean that it was very unsuccessful. their disastrous performance in the general election of 1906. + disastrously dis·as·trous·ly the company's disastrously timed venture into property development. very bad, or ending in failure
() From French désastreux, from Middle French desastre (modern désastre) 'disaster', from Italian disastro, itself from dis- "away, without" (from Latin) + astro "star, planet" (from Latin astrum 'star, celestial body', from Ancient Greek (astron)).