Synonyms: huge, enormous, gigantic, very big, very large, great, giant, colossal, mammoth, vast, immense, tremendous, mighty, stupendous, monumental, epic, prodigious, mountainous, monstrous, titanic, towering, elephantine, king-sized, king-size, gargantuan, Herculean, Brobdingnagian, substantial, extensive, hefty, bulky, weighty
Antonyms: Tiny, small
1. large and heavy or solid.
2. exceptionally large.
This is the massive structure I have ever seen.