Synset

(of events) having extremely unfortunate or dire consequences; bringing ruin
<adj.all>   freq. cnt.: 8 freq. cnt.: 6 freq. cnt.: 2

black

calamitous

disastrous

fatal

fateful

sample sentences

"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"