1) Alarming 2) Awful 3) Dire 4) Direful 5) Dread 6) Dreaded 7) Dreadful 8) Fearful 9) Fearsome 10) Frightening 11) Horrific 12) Shockingly dreadful 13) Terrible 1) Alarming 2) Awful 3) Direful 4) Disgusting 5) Dread 6) Dreaded 7) Dreadful 8) Fearful 9) Fearsome 10) Frightening 11) Horrific 12) Horrifying 13) Intolerable 14) Terrible 
• (a.) Fearful; frightful.
Hor·ren'dous adjective [ Latin horrendus .] Fearful; frightful. [ Obsolete] I. Watts. 
horrendous 1. Sufficiently unpleasant, frightening, or shocking so as to provoke horror. 2. Very large, great, or high, often unreasonably or excessively so. 3. Hideous; dreadful; shockingly dreadful; horrible.
shockingly dreadful; horrible: a horrendous crime.
causing fear or dread or terror