horrendous (adj.)

• appalling
• astounding
• atrocious
• awe-inspiring
• awesome
• awful
• baneful
• beastly
• dire
• direful
• dread
• dreaded
• dreadful
• fell
• formidable
• ghastly
• ghoulish
• grim
• grisly
• gruesome
• hideous
• horrible
• horrid
• horrific
• horrifying
• macabre
• morbid
• redoubtable
• rotten
• shocking
• terrible
• terrific
• tragic
• tremendous
• unspeakable