blæk kəˈlæmɪtəs dɪˈzɑːstɹəs ˈfeɪtəl ˈfeɪtfəl (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 it is fatal to enter any war without the will to win it a fateful error