Hideous is a word that means extremely ugly. Anything or anybody that is painful — and a little scary — to look at is hideous.
This is a strong word. If you have a zit on your nose, you might feel hideous, but you're probably not. Only terrifyingly ugly people and things are truly hideous. In horror movies, the special effects team tries to make the monsters hideous, so moviegoers will be scared. This word can also be a more general term for awful things. For example, you could say the effects of a concussion are so severe that they're hideous.