1. (a.) Containing portents; foreshadowing; ominous\.

2. (a.) Hence: Monstrous; prodigious; wonderful; dreadful; as, a beast of portentous size.

alarming amazing apocalyptic astonishing astounding awe-inspiring awesome bad baleful baneful black bodeful boding dark dire doomful dreary earnest evil evil-starred exceptional extraordinary fabulous fantastic fatal fateful foreboding forerunning forewarning formidable gloomy grave heavy ill ill-boding ill-fated ill-omened ill-starred imposing inauspicious indescribable ineffable legendary lowering marvelous menacing mind-boggling miraculous momentous mythical noteworthy of evil portent ominous phenomenal portending precautional precautionary precursive precursory premonitory prodigious prodromal prodromic remarkable serious sinister sober solemn somber star-crossed stupefying stupendous threatening unexampled unfavorable unfortunate unlucky unparalleled unprecedented unpromising unpropitious unspeakable untoward weighty wonderful wondrous