ominous

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.