fateful

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”

of ominous significance

(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”

controlled or decreed by fate; predetermined

• “a fatal series of events”