Double means twice as much or two times the amount of something. If you have five dollars and someone gives you double that, you now have ten dollars. When a recipe calls for double the sugar, you use two times as much as it originally asked for.

The word works in many ways. In baseball, a double is when a batter hits the ball and safely reaches second base. When you see double, your vision makes one object look like two (which sometimes happens if you spin around too fast). A double can also mean a person who looks exactly like someone else, especially someone hired to take an actor's place in a movie during dangerous scenes.

Double can describe things that have two parts or layers. A double-decker bus has two levels for passengers. A double bed is wider than a single bed, meant for two people. When you do something on the double, you do it very quickly, like you're moving twice as fast as normal.

The word appears in phrases too: double-check means to verify something twice to make sure it's correct, and double-cross means to betray someone who trusted you. When something increases dramatically, we say it doubled, like when a lemonade stand's profits double from one week to the next.