The term SIGN OF IMPENDING DOOM can be summarized by the crossword solution of OMEN, which is a four-letter word. An OMEN is an event or occurrence that is believed to portend a good or bad outcome in the future. It is often seen as a warning or foreshadowing of something to come. In many cultures, omens are seen as a sign of impending doom, and are interpreted as a warning to take caution or prepare for the worst.