Synonyms for Massive (same or very similar meaning)
WordNet sense 1 (entirely of one substance with no holes inside):
solidWordNet sense 2 (imposing in size or bulk or solidity):
monolithic, monumentalWordNet sense 3 (above average in size or number or quantity or magnitude or extent):
bigWordNet sense 4 (of comparatively great physical weight or density):
heavyFrom the ODE community, based on WordNetadd/edit