Portentous means ominous or warning of something important, often something bad, about to happen. When dark storm clouds gather and the wind suddenly stops, creating an eerie silence, that stillness feels portentous because it suggests a severe storm is coming. When a character in a story discovers a mysterious symbol carved into an ancient door, the moment feels portentous because readers sense it signals danger ahead.

The word carries a sense of weight and foreboding. A portentous dream might fill you with unexplained worry about the next day. A portentous silence might fall over a classroom just before the teacher announces a surprise test. The mood is serious, heavy, almost like the air itself is trying to warn you.

Sometimes people use portentous to describe someone acting overly serious or self-important, as if everything they say carries earth-shattering significance. A student might speak in a portentous tone about a minor disagreement, acting like it's the most important conflict in history. This usage is slightly mocking, suggesting someone is being more dramatic than the situation deserves.