A portent is a sign or warning that something important or dramatic is about to happen, usually something bad. When dark clouds gather suddenly on a sunny afternoon, some might see them as a portent of a coming storm. In Shakespeare's play Julius Caesar, a fortune teller warns Caesar to “beware the Ides of March,” a portent of the danger waiting for him.

The word carries a sense of foreboding, that feeling you get when something seems off or ominous. If your normally cheerful teacher walks in looking unusually serious, you might see it as a portent of a difficult pop quiz. Ancient Romans believed that unusual events like comets, eclipses, or birds flying in strange patterns were portents sent by the gods.

A portent differs from an ordinary prediction because it feels more mysterious and serious. Weather forecasts predict rain, but seeing a red sky at dawn can feel like a portent. The word suggests something momentous is coming, something that will change things significantly.

Something described as portentous carries this same quality of warning or importance, though the word can also mean pompous or self-important, like someone acting overly serious about something trivial.