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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.
Origin
1970-1975
1970-75
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for leap seconds

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
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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leap seconds in Science
leap second
  (lēp)   
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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leap seconds in Culture

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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6
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