Thesaurus

Synonyms for Monstrous include:

ample, astronomic, astronomical, atrocious, awkward, bad, banging, bear-sized, big, bigger, biggish, black, blown-up, bouffant, broad, Brobdingnagian, bulky, capacious, colossal, corruptive, cosmic, dark, deep, demonic, despicable, devilish, diabolic, diabolical, disfigured, displeasing, double, elephantine, enlarged, enormous, epic, evil, evil-looking, evil-minded, extended, extensive, fiendish, flagitious, fugly, full-size, galactic, gargantuan, giant, gigantic, grand, great, grievous, grotesque, heinous, hellish, heroic, hideous, huge, hulking, hulky, humongous, ill-favored, ill-favoured, immense, immoral, infernal, jumbo, king-size, king-sized, large, large-mouthed, large-scale, larger, larger-than-life, largish, life-size, life-sized, lifesize, macro, mammoth, man-sized, massive, medium-large, mephistophelean, mephistophelian, monolithic, monstrous, monumental, mountainous, offensive, outsize, outsized, overlarge, oversize, oversized, perversive, pestiferous, plumping, prodigious, puffy, queen-size, queen-sized, rangy, repulsive, satanic, scrofulous, sinister, sizable, sizeable, slimy, spacious, stupendous, super, thumping, titanic, too large, tremendous, ugly, unattractive, unholy, unlovely, unnatural, unpicturesque, unrighteous, unsightly, unworthy, vast, vile, volumed, voluminous, walloping, whacking, whopping, wicked, wide, wide-ranging, worthless, wretched, wrong

monstrous is a ADJ.