hideous means very ugly. monstrous means "like a monster" (either big, or ugly, or powerful, or deadly, etc).

'hideous' and 'monstrous' ? Hideous is very ugly. Monstrous is very scary. The words can be used interchangeably in certain cases. The hideous witch called forth a monstrous demon from the pit of Ghana to devour the weary traveler just as he was about to run away. The monstrous witch called forth a hideous demon from the pit of Ghana to devour the weary traveler just as he was about to run away.

two words of similar meaning but I think monstrous mean to scare or to avoid it. where as hideous mean ugly but not necessary enough to give me a fright. example that guy looks hideous (I'm not going to run just because he's ugly). The thing was monstrous (Implies that ugly or not I was willing to keep my distance).

They are similar: hideous –adjective 1. horrible or frightful to the senses; repulsive; very ugly: a hideous monster. 2. shocking or revolting to the moral sense: a hideous crime. 3. distressing; appalling: the hideous expense of moving one's home to another city. monstrous –adjective 1. frightful or hideous, esp. in appearance; extremely ugly. 2. shocking or revolting; outrageous: monstrous cruelty. 3. extraordinarily great; huge; immense: a monstrous building. 4. deviating grotesquely from the natural or normal form or type. 5. having the nature or appearance of a fabulous monster. –adverb 6. extremely; exceedingly; very.

hideous: disgusting monstrous:enormous