A clock is an instrument, for example in a room or on the outside of a building, that shows what time of day it is.

A time clock in a factory or office is a device that is used to record the hours that people work. Each worker puts a special card into the device when they arrive and leave, and the times are recorded on the card.

In a car, the clock is the instrument that shows the speed of the car or the distance it has travelled.

To clock a particular time or speed in a race means to reach that time or speed.

If something or someone is clocked at a particular time or speed, their time or speed is measured at that level.

If you clock something, you notice or see it.

If you are doing something against the clock, you are doing it in a great hurry, because there is very little time.

If you beat the clock, you finish doing something or succeed in doing something before the time allowed for doing it has ended.

If something is done round the clock or around the clock, it is done all day and all night without stopping.

If you want to turn the clock back or put the clock back, you want to return to a situation that used to exist, usually because the present situation is unpleasant.

If you are watching the clock, you keep looking to see what time it is, usually because you are bored by something and want it to end as soon as possible.