Clack is a sharp, hard sound that happens quickly and often repeatedly, like when you snap wooden blocks together or type rapidly on a keyboard. It's the sound of hard things hitting each other: the clack-clack-clack of a train rolling over railroad tracks, or the clack of billiard balls colliding during a pool game.

The word also means to make this sound. Shoes with hard heels clack across a tile floor. When you're nervous, you might clack your teeth together. Old-fashioned typewriters would clack loudly with each keystroke, and some people today prefer mechanical keyboards precisely because they clack satisfyingly when you type.

Clack is one of those wonderful words that sounds like what it means. Say it out loud and you'll hear that sharp, crisp sound built right into the word itself. It's similar to click or clunk, but sharper and lighter. A door might click shut gently, clunk shut heavily, or clack shut quickly and sharply.