Dictionary.com

light-year

[ lahyt-yeer, -yeer ]
/ ˈlaɪtˌyɪər, -ˈyɪər /
Save This Word!

noun
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
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.

COMPARE MEANINGS

Click for a side-by-side comparison of meanings. Use the word comparison feature to learn the differences between similar and commonly confused words.
QUIZ
SHALL WE PLAY A "SHALL" VS. "SHOULD" CHALLENGE?
Should you take this quiz on “shall” versus “should”? It should prove to be a quick challenge!
Question 1 of 6
Which form is commonly used with other verbs to express intention?

Origin of light-year

First recorded in 1885–90
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022

How to use light-year in a sentence

British Dictionary definitions for light-year

light year

noun
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
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

Scientific definitions for light-year

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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for light-year

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.

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.
FEEDBACK