You use double to indicate that something includes or is made of two things of the same kind.

You use double before a singular noun to refer to two things of the same type that occur together, or that are connected in some way.

If something is double the amount or size of another thing, it is twice as large.

You use double to describe something which is twice the normal size or can hold twice the normal quantity of something.

A double room is a room intended for two people, usually a couple, to stay or live in.

A double bed is a bed that is wide enough for two people to sleep in.

You use double to describe a drink that is twice the normal measure.

Double is used when you are spelling a word or telling someone a number to show that a letter or digit is repeated.

When something doubles or when you double it, it becomes twice as great in number, amount, or size.

If you refer to someone as a person's double, you mean that they look exactly like them.

If a person or thing doubles as someone or something else, they have a second job or purpose as well as their main one.

In tennis or badminton, when people play doubles, two teams consisting of two players on each team play against each other on the same court.

If you do something at the double or on the double, you do it very quickly or immediately.

When you bend double, you bend the top half of your body downwards a long way.

If you are bent double, the top half of your body is bent downwards so that your head is close to your knees.

If you are seeing double, there is something wrong with your eyes, and you can see two images instead of one.