light-year

[lahyt-yeer, -yeer]
noun
1.
Astronomy. the distance traversed by light in one mean solar year, about 5.88 trillion mi. (9.46 trillion km): used as a unit in measuring stellar distances. Abbreviation: lt-yr
2.
light-years.
a.
a very great distance, especially in development or progress: The new computer is light-years ahead of the old one.
b.
a very long time: It's been light-years since I've seen my childhood friends.

Origin:
1885–90

Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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Collins
World English Dictionary
light year
 
n
a unit of distance used in astronomy, equal to the distance travelled by light in one year, i.e. 9.4607 × 1012 kilometres or 0.3066 parsecs

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Etymonline
Word Origin & History

light year
also light-year, lightyear, "distance light travels in one year," 1888, from light (n.) + year.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
light-year  
The distance that light travels in a vacuum in one year, equal to about 9.46 trillion km (5.88 trillion mi). Light-years are used in measuring interstellar and intergalactic distances. Compare astronomical unit, parsec.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary

light year definition


The distance traveled by light in a year (over five trillion miles); a unit for measuring distances outside the solar system. The star nearest to our sun, Alpha Centauri, is more than four light years away.

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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Example sentences
That's something this franchise seemed a light year away from one calendar year ago.
Planetary nebulae, even large ones, are usually only a light year or two across.
Newt has a stack of baggage a light year tall and is volatile and untrustworthy.
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