Synonyms for Gargantuan:

adj.

large (adjective)
capacious, cavernous, colossal, tremendous, ample, humongous, extensive, massive, elephantine, majestic, expansive, huge, magnificent, big, lofty, bulky, great, mammoth, impressive, immense, enormous, comprehensive, princely, roomy, gigantic, large, copious, baggy, voluminous, spacious, soaring, prodigious, grandiose, awesome, generous, grand, sizable, vast, giant, towering.
very large (adjective)
enormous, mammoth, giant, huge, immense, massive, elephantine, jumbo, whopping, mountainous, humongous, prodigious, towering, vast, titanic, tremendous, monstrous, gigantic, big, monumental, colossal.

n.

wide, high. herculean, mountainous, Bunyanesque, Pythonic, heroic, stupendous, monstrous, monumental, whopping, Massy, titanic, Gigantesque, behemoth, mighty, mastodonic, Brobdingnagian, cyclopean, walloping, monster. gargantuan (noun)
elephantine, large, big, jumbo, giant.

Other synonyms:

cyclopean, Brobdingnagian, Pythonic, mastodonic, Bunyanesque, Massy, Gigantesque, walloping. mountainous, monumental, whopping, titanic. heroic, herculean, stupendous, monstrous. mighty. monster. Other relevant words:
heroic, stupendous, jumbo, monster, monumental, titanic, herculean, mountainous, mastodonic, wide, monstrous, Brobdingnagian, Massy, Bunyanesque, Gigantesque, Pythonic, walloping, mighty, behemoth, whopping, cyclopean.

Usage examples for gargantuan

  1. Swell to gargantuan heights , I shake courage off bravado? – NATURAE by Dom