light years

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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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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