leap second

American  

noun

1. an extra second intercalated into the world's timekeeping system about once a year, made necessary by the gradual slowing down of the earth's rotation.

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leap second British  

noun

1. a second added to or removed from a scale for reckoning time on one particular occasion, to synchronize it with another scale

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leap second Scientific  

/ lēp /

1. A second of time, as measured by an atomic clock, added to or omitted from official timekeeping systems annually to compensate for changes in the rotation of the Earth.

2. See more at coordinated universal time

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leap second Cultural  

1. A second inserted into the year to make up for the fact that the Earth's rotation is slowing down.

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Discover More

Scientists know when to insert a leap second by comparing the Earth's rotation to an atomic clock.

Etymology

Origin of leap second

First recorded in 1970–75

Example Sentences

This is known as a "negative leap second."

From BBC • Mar. 28, 2024

There’s even a leap second occasionally, but there’s no hullabaloo when that happens.

From Seattle Times • Feb. 24, 2024

Devised in 1972 and used 27 times since, the leap second wreaks havoc with modern-day telecommunications, banking, and other networks.

From Science Magazine • Nov. 30, 2022

Future metrologists might find more elegant ways than the leap second to realign UTC and UT1.

From Scientific American • Nov. 22, 2022

Steps remain in the elimination of the leap second.

From New York Times • Nov. 19, 2022