Fast means moving or happening at high speed. A cheetah runs fast when it sprints across the savanna at 70 miles per hour. A fast reader zooms through books, finishing them quickly. When you're running late and dash to catch the school bus, you're moving fast.

Fast can describe how quickly something happens (a fast response) or how soon it arrives (fast delivery). Your reflexes are fast if you can catch a ball before it hits the ground. A fast computer processes information in seconds rather than minutes.

The word also means firmly fixed or held securely in place. When you make a boat fast to a dock, you tie it so it won't drift away. If a drawer is stuck fast, it won't budge no matter how hard you pull. Colors that are colorfast won't fade or run when washed.

Fast also means to go without food, usually for religious or health reasons. Many religions include periods of fasting as a spiritual practice. When you fast, you intentionally skip meals for a specific time. Muslims fast from dawn to sunset during the holy month of Ramadan.

Notice how fast asleep means sleeping deeply and soundly, which connects to that idea of being firmly fixed. You're not quickly asleep. You are solidly asleep, hard to wake up.