1) Arousing amazement 2) Important 3) Ominous or fateful 4) Ominous, fateful 5) Ominously prophetic 6) Ominously significant 7) Overblown 8) Prodigious 9) Puffed up with vanity 10) Significant 1) Boding 2) Foreboding 3) Oracular 4) Overblown 5) Pompous 6) Pretentious 7) Prophetic 8) Prophetical 9) Significant 10) Threatening 
• (a.) Hence: Monstrous; prodigious; wonderful; dreadful; as, a beast of portentous size. • (a.) Of the nature of a portent; containing portents; foreshadowing, esp. foreshadowing ill; ominous.
Por·tent'ous adjective [ Latin portentosus .] 1. Of the nature of a portent; containing portents; foreshadowing, esp. foreshadowing ill; ominous. « For, I believe, they are portentous things.» Shak. « Victories of strange and almost portentous s...
[adj] - of momentous or ominous significance
portentous 1. That which portends evil; ominous. 2. Arousing awe or amazement; marvelous; prodigious.
prodigious adjective of momentous or ominous significance; `such a portentous...monster raised all my curiosity`- Herman Melville; `a prodigious vision`
[SAT terms] of momentous or ominous significance