Definition of vast :
1. A waste region; boundless space; immensity.
2. Of great extent; very spacious or large; also, huge in bulk; immense; enormous; as, the vast ocean; vast mountains; the vast empire of Russia.
3. Very great in importance; as, a subject of vast concern.
4. Very great in numbers, quantity, or amount; as, a vast army; a vast sum of money.
5. Waste; desert; desolate; lonely.
widespread, broad, Bunyanesque, detailed, far-flung, pythonic, mighty, jumbo, stupendous, abundant, whopping, commodious, astronomical, mountainous, long, titanic, wide, Cyclopean, monstrous, coarse, gigantesque, considerable, mastodonic, far-reaching, walloping, prolonged, behemoth, limited, monumental, narrow, massy, all-inclusive, Herculean, monster, heroic, Brobdingnagian
infinite (part of speech: adjective)
large (part of speech: adjective)
extensive, roomy, ample, large, lofty, colossal, sizable, magnificent, generous, enormous, big, voluminous, humongous, great, copious, awesome, giant, gargantuan, expansive, baggy, impressive, bulky, capacious, immense, spacious, grand, cavernous, majestic, comprehensive, towering, princely, prodigious, tremendous, mammoth, huge, elephantine, gigantic, massive, soaring, grandiose
- The room was vast- too big for comfort. - "This Crowded Earth", Robert Bloch.
- Murray, the secretary, passed his hand over his wrinkled forehead and sighed, as if he himself had made away with the vast sum of money, and the lawyer frowned and shuffled the papers before him. - "At Love's Cost", Charles Garvice.
- Nothing much else is vast, except once in a while a distance. - "Patty Blossom", Carolyn Wells.