Synonyms for Massive:

adj.

all (adjective)
monumental, monolithic.
heavy (adjective)
leaden, oppressive, gravitational, pressing, dense, ponderous, weighty, heavy.
large (adjective)
huge, soaring, colossal, monumental, extensive, tremendous, prodigious, ponderous, sizable, cumbersome, elephantine, giant, gigantic, towering, awesome, majestic, monster, large, heavy, big, whopping, immense, mountainous, walloping, enormous, bulky, lofty, great, cavernous, mammoth, mighty, generous, capacious, titanic, hefty, princely, voluminous, vast, spacious, impressive, magnificent, expansive, substantial, roomy, comprehensive, grand, baggy, ample, solid, grandiose, gargantuan, humongous, copious, weighty.
strong (adjective)
hefty.

n.

cumbersome, study at heavy, substantial, widely. serious, extreme, rigorous, oversized, dire, awful, acute, oversize, severe, profound, grave, desperate. organization, commission, heavyweight, hefty, club, panel, association, police, flash mobbing, flash mob, Support Group. monster, titanic, excellent, cyclopean, incredible, jumbo, decent, Bunyanesque, Gigantesque, stupendous, fine, good, wonderful, monstrous, mighty, wonder, superb, behemoth, walloping, mastodonic, heroic, whopping, Massy, mountainous, herculean, exceptional, Pythonic, Brobdingnagian. high. massive (noun)
monolithic, big, solid, large, heavy, monumental.

Other synonyms:

Brobdingnagian, oversize, oversized, walloping, heavyweight, Gigantesque, cyclopean, Massy, mastodonic, Bunyanesque, Pythonic. titanic, whopping, mountainous. herculean, stupendous, heroic, monstrous. mighty. monster. Other relevant words:
monolithic, Massy, monster, profound, heroic, awful, acute, incredible, oversized, serious, panel, Bunyanesque, club, whopping, substantial, grave, monstrous, decent, extreme, monumental, severe, titanic, fine, police, high, dire, good, association, Gigantesque, cyclopean, commission, wonder, desperate, hefty, Brobdingnagian, oversize, solid, jumbo, behemoth, stupendous, walloping, widely, mastodonic, Pythonic, rigorous, heavyweight, mountainous, excellent, mighty, organization, superb, exceptional, herculean, cumbersome, wonderful.