portentous

portentous (Eliciting amazement), adjective amazing, astonishing, breathtaking, exceptional, extraordinary, great, inconceivable, incredible, indescribable, marvelous, miraculous, notable, noteworthy, novel, out of the orrinary, outstanding, phenomenal, prodigal, prodigious, rare, remarkable, shocking, singular, staggering, startling, stirring, striking, stupendous, superb, superlative, surprising, tremendous, uncustomary, unexampled, unheard of, unique, unparalleled, unprecedented, unusual, wonderful, wondrous

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portentous (Ominous), adjective alarming, augural, augurous, baleful, black, bodeful, boding, cautionary, dark, dire, direful, divinatory, doomful, dread, dreadful, dreary, fateful, fatiloquent, fearful, forbidding, foreboding, forewarning, forthcoming, frightening, frightful, gloomy, grim, haunting, heralding, ill-boding, ill-fated, inauspicious, indicative, intimidating, mantic, minacious, minatorial, minatory, monitory, ominous, oracular, perilous, portending evil, premonitive, presageful, presaging, presentient, prophetic, prophetical, pythonic, sibylline, sinister, somber, suggestive, threatening, unpropitious

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See also: dire, imminent, important, ominous, oracular, presageful, prophetic, unusual