WordNet sense 1 (of momentous or ominous significance):

portentous

WordNet sense 2 (important in effect or meaning):

important, significant

WordNet sense 3 (far beyond what is usual in magnitude or degree):

exceeding, exceptional, surpassing, Olympian

WordNet sense 4 (beyond what is ordinary or usual; highly unusual or exceptional or remarkable):

extraordinary

WordNet sense 5 (so great in size or force or extent as to elicit awe):

colossal, stupendous

WordNet sense 6 (above average in size or number or quantity or magnitude or extent):

big, large