frightful or hideous, esp. in appearance; extremely ugly.

shocking or revolting; outrageous

monstrous cruelty.

extraordinarily great; huge; immense

a monstrous building.

deviating grotesquely from the natural or normal form or type.

having the nature or appearance of a fabulous monster.

extremely; exceedingly; very.

noun

atrociousness , atrocity , heinousness