adjective

causing or likely to cause horror; shocking.

a horrible massacre

dreadful,horrifying,horrific,horrendous,frightful,fearful,awful,terrible,shocking,appalling,hideous,grim,grisly,ghastly,harrowing,gruesome,heinous,vile,nightmarish,macabre,unspeakable,hair-raising,spine-chilling,loathsome,monstrous,abhorrent,detestable,hateful,execrable,abominable,atrocious,sickening,nauseating