leap seconds

leap second

noun
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.

Origin:
1970–75

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World English Dictionary
leap second
 
n
a second added to or removed from a scale for reckoning time on one particular occasion, to synchronize it with another scale

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
leap second   (lēp)  Pronunciation Key 
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. See more at coordinated universal time.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary

leap second definition


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

Note: Scientists know when to insert a leap second by comparing the Earth's rotation to an atomic clock.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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