leap second

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.

leap second

noun

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

leap second

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

leap second

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

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

Word History and Origins

Origin of leap second¹

First recorded in 1970–75