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The idiom "round the clock" means working or operating continuously for a long period of time, especially 24 hours a day. It can also refer to providing service around the clock, such as a restaurant or gas station that stays open all night.
The phrase "round the clock" can be traced back to the 17th century, where it was used in a literal sense to describe objects that were made or designed to last for an entire day. Over time, the idiom began to be used figuratively to describe activities that were done continuously throughout the day or night. In the early 20th century, the phrase became associated with workers who were required to work long hours, and by the mid-20th century it had taken on its current meaning of providing service or operations around the clock.