Stupendous means extraordinarily impressive or amazingly large. When something is stupendous, it makes you catch your breath and think “Wow!” The Grand Canyon is stupendous in its size and beauty. A gymnast might perform a stupendous routine that leaves the whole crowd on their feet, cheering.

The word suggests something that goes beyond ordinary greatness. A good science project might earn an A, but a stupendous one makes everyone gather around to see how you built a working model of the solar system with motorized planets. A regular rainstorm gets you wet, but a stupendous thunderstorm makes the whole sky light up and the ground shake.

You might hear people describe a stupendous victory when a team wins by an overwhelming margin, or a stupendous discovery when scientists find something that changes what we know about the world. The word carries a sense of awe: whatever is stupendous doesn't just get your attention, it genuinely astonishes you.