What is the synonym of horrible?

There are many synonyms for "horrible," depending on the specific nuance you want to convey. Here are a few options, ranging from general to more specific:

General:

* Awful

* Terrible

* Dreadful

* Frightful

* Appalling

* Atrocious

* Gruesome

* Abominable

* Repulsive

* Disgusting

More specific:

* For appearance: Hideous, ugly, grotesque

* For experience: Painful, agonizing, unbearable

* For situation: Catastrophic, disastrous, calamitous

* For actions: Cruel, vicious, brutal

The best synonym depends on the context of your sentence and the specific emotion you want to evoke.