Synonyms for Monstrous:

adj.

atrocious (adjective)
bad, nefarious, shocking, wicked.
colossal (adjective)
cyclopean, jumbo, mountainous.
corrupt (adjective)
baneful.
cruel (adjective)
hard, hateful, sinful, unkind, unnatural.
detestable (adjective)
offensive, repugnant, revolting.
different (adjective)
unusual.
evil (adjective)
abominable, atrocious, bad, baneful, calamitous, damnable, destructive, detrimental, disgraceful, evil, foul, heinous, hideous, loathsome, nefarious, offensive, repellent, reprehensible, repugnant, repulsive, revolting, sinful, sinister, terrible, wicked.
monstrous (adjective)
abnormal, atrocious, colossal, cruel, disgraceful, elephantine, enormous, evil, flagitious, foul, freakish, gargantuan, giant, gigantic, grotesque, heinous, hideous, huge, immense, inhuman, loathsome, mammoth, massive, monumental, outrageous, prodigious, scandalous, stupendous, terrible, titanic, tremendous, uncanny, unusual, vast, whopping.
offensive (adjective)
outrageous.

adv.

beastly (adverb)
abominable, repulsive.

n.

cruel, enormous, hard, hateful, inhuman, pitiless, prodigious, stupendous, uncharitable, unkind. grim, outrageous, plain, right, scandalous, shocking. behemoth, colossal, cyclopean, elephantine, gargantuan, giant, gigantic, herculean, heroic, huge, immense, jumbo, mammoth, massive, mighty, monster, monumental, mountainous, titanic, tremendous, vast, walloping, whopping, Brobdingnagian, Gigantesque, Massy, Pythonic, Bunyanesque, mastodonic. freakish, freaky, usual. monstrous (noun)
atrocious, big, evil, flagitious, grievous, grotesque, heinous, large, ugly, unnatural, wicked.
shocking (noun)
outrageous.
unnatural (noun)
abnormal, uncanny, unusual.

Other synonyms:

cyclopean, elephantine, enormous, freaky, hateful, inhuman, pitiless, prodigious, uncharitable, unkind, walloping, Brobdingnagian, Gigantesque, Massy, Pythonic, Bunyanesque, mastodonic. colossal, gargantuan, gigantic, hard, huge, immense, monumental, mountainous, scandalous, shocking, titanic, tremendous, vast, whopping. freakish, herculean, heroic, stupendous. massive, mighty. grim, monster, plain. vicious
cruel.
Other relevant words:
abnormal, abominable, behemoth, big, colossal, cruel, cyclopean, elephantine, enormous, flagitious, freakish, freaky, gargantuan, giant, gigantic, grievous, grim, grotesque, hard, hateful, herculean, heroic, huge, immense, inhuman, jumbo, large, mammoth, massive, mighty, monster, monumental, mountainous, outrageous, pitiless, plain, prodigious, right, scandalous, shocking, stupendous, titanic, tremendous, ugly, uncanny, uncharitable, unkind, unnatural, unusual, usual, vast, walloping, whopping, Brobdingnagian, Gigantesque, Massy, Pythonic, Bunyanesque, mastodonic.

Usage examples for monstrous

  1. We should accept the evidence that some monstrous herd, making its way through a mountain pass, somehow went crazy and bolted for the plains. – This World Is Taboo by Murray Leinster