Suddenly means happening quickly and unexpectedly, without warning. When something occurs suddenly, there's no gradual build-up or advance notice. One moment everything is normal, and the next moment, something has changed.

If you're reading quietly in your room and suddenly hear a loud crash downstairs, that noise arrived without any hint it was coming. When a friend suddenly appears beside your locker when you thought you were alone, they startled you because you didn't see them approaching. A sudden rainstorm is one that starts pouring without the slow gathering of clouds you might have noticed.

The word captures that jarring feeling when something interrupts the expected flow of events. A teacher might suddenly announce a pop quiz. A character in a story might suddenly realize the solution to a mystery. Weather can change suddenly. Ideas can strike suddenly.

Suddenly is the opposite of gradually or slowly. Things that happen suddenly catch us off guard, which is why the word often appears in exciting moments in stories. “Suddenly, the door burst open” creates more drama than “The door slowly creaked open.”