adjective

causing great horror or fear.

one of the most ghastly crimes ever committed

terrible,frightful,horrible,grim,awful,dire,frightening,terrifying,horrifying,alarming,distressing,shocking,appalling,harrowing,dreadful,fearful,hideous,horrendous,monstrous,unspeakable,gruesome,tragic,calamitous,grievous,grisly,serious,severe,grave,very bad,unforgivable,inexcusable,indefensible,reprehensible,disgraceful,shameful,parlous