ominous

UK: /ˈɒmɪnəs/ US: /ˈɑmənəs/ ,(om′ə nəs)

WordReference Random House Learner's Dictionary of American English © 2025

om•i•nous /ˈɑmənəs/   adj. 

1. foreboding;
   threatening:
   ominous black clouds.

om•i•nous•ly, adv. 
om•i•nous•ness, n. [uncountable]

WordReference Random House Unabridged Dictionary of American English © 2025

om•i•nous  (om′ə nəs), adj. 

1. portending evil or harm;
   foreboding;
   threatening;
   inauspicious:
   an ominous bank of dark clouds.
2. having the significance of an omen.

• Latin ōminōsus portentous, equivalent. to ōmin- (stem of ōmen) omen + -ōsus -ous
• 1580–90

om′i•nous•ly, adv. 
om′i•nous•ness, n. 
Synonyms

Ominous, portentous, threatening, menacing, fateful are adjectives describing that which forebodes a serious, significant, and often harmful outcome. Ominous, derived from omen "a predictor of outcomes,'' usually suggests evil or damaging eventualities:
ominous storm clouds; an ominous silence.
Portentous, although it may suggest evil results, often stresses a momentous or very important outcome:
a portentous moment in history; a portentous escalation of hostilities.
Threatening may suggest calamity or great harm but sometimes mere unpleasantness:
a threatening rumble from the volcano; A threatening look from his brother caused him to quickly change the subject.
Menacing always suggests serious damage as an outcome:
a disease menacing the entire population; He advanced with a menacing swagger.
Fateful most often stresses the great or decisive importance of what it describes:
a fateful encounter between two future leaders; a fateful day that changed our world.

Collins Concise English Dictionary © HarperCollins Publishers::

ominous / ˈɒmɪnəs/ adjective

1. foreboding evil
2. serving as or having significance as an omen

Etymology: 16th Century: from Latin ōminōsus, from omen

ˈominously adverb

ˈominousness noun