Synonyms for Tremendous (same or very similar meaning)
WordNet sense 1 (extreme in degree or extent or amount or impact):
awful, frightful, terrible
WordNet sense 2 (extraordinarily good; used especially as intensifiers):
fantastic, grand, howling, marvelous, rattling, terrific, wonderful, wondrous, marvellous
WordNet sense 3 (beyond what is ordinary or usual; highly unusual or exceptional or remarkable):
extraordinary
WordNet sense 4 (extraordinarily large in size or extent or amount or power or degree):
enormous
WordNet sense 5 (above average in size or number or quantity or magnitude or extent):
large
From the ODE community, based on WordNet
add/edit