portentous

1 being or showing a sign of evil or calamity to come an eerie and portentous stillness hung over the camp the night before the battle Synonyms baleful, dire, direful, doomy, foreboding, ill, ill-boding, inauspicious, menacing, minatory, ominous, sinister, threateningRelated Words black, bleak, cheerless, chill, Cimmerian, cloudy, cold, comfortless, dark, darkening, depressing, depressive, desolate, dim, disconsolate, dismal, drear, dreary, dreich [chiefly Scottish], elegiac (also elegiacal), forlorn, funereal, gloomy, glum, godforsaken, gray (also grey), lonely, lonesome, lugubrious, miserable, morbid, morose, murky, plutonian, saturnine, sepulchral, somber (or sombre), sullen, sunless, tenebrific, tenebrous, wretched; discouraging, disheartening, hopeless, unfavorable, unpromising, unpropitious; ill-fated, ill-starred, star-crossed, troubled, unfortunate, unlucky; evil, malign, malignantNear Antonyms auspicious, benign, bright, encouraging, favorable, golden, heartening, hopeful, promising, propitious, prosperousAntonyms unthreatening

2 causing wonder or astonishment in 1969 people regarded the first landing on the moon as a truly portentous event Synonyms amazing, astonishing, astounding, awesome, awful, eye-opening, fabulous, miraculous, marvelous, prodigious, staggering, stunning, stupendous, sublime, surprising, wonderful, wondrousRelated Words incomprehensible, inconceivable, incredible, unbelievable, unimaginable, unthinkable; extraordinary, phenomenal, rare, sensational, spectacular; singular, uncommon, unique, unusual, unwonted; conspicuous, notable, noticeable, outstanding, remarkable; impressive, smashing, striking; mind-bending, mind-blowing, mind-boggling; animating, energizing, enlightening, enlivening, exciting, galvanizing, invigorating, stimulating; alluring, attracting, attractive, beguiling, bewitching, captivating, charming, enchanting, entertaining, enthralling, fascinating, interestingNear Antonyms unimpressive, uninspiring, unremarkable; boring, dull, jading, monotonous, tedious, tiring, uninspired, uninteresting, wearisome, weary, wearying; common, customary, mundane, normal, ordinary, typical, unexceptional, usual; draining, enervating, exhausting, fatiguing, wearing; debilitating, enfeebling; demoralizing, discouraging, disheartening, dispiriting