adjective

causing or involving great suffering, fear, or unhappiness; extremely bad or serious.

there’s been a dreadful accident

terrible,frightful,horrible,grim,awful,dire,frightening,terrifying,horrifying,alarming,distressing,shocking,appalling,harrowing,ghastly,fearful,hideous,horrendous,monstrous,unspeakable,gruesome,tragic,calamitous,grievous,grisly,terrific