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light-year

[lahyt-yeer, -yeer]
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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,
    1. a very great distance, especially in development or progress: The new computer is light-years ahead of the old one.
    2. a very long time: It's been light-years since I've seen my childhood friends.
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Origin of light-year

First recorded in 1885–90
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for light year

light year

noun
  1. a unit of distance used in astronomy, equal to the distance travelled by light in one year, i.e. 9.4607 × 10 12 kilometres or 0.3066 parsecs
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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

Word Origin and History for light year

n.

also light-year, lightyear, "distance light travels in one year," 1888, from light (n.) + year.

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Online Etymology Dictionary, © 2010 Douglas Harper

light year in Science

light-year

  1. 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.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

light year in Culture

light year

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.

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The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.