[lahyt-yeer, -yeer]


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
  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.

Origin of light-year

First recorded in 1885–90 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for light-year

Contemporary Examples of light-year

Historical Examples of light-year

  • The figures of the Light-year dials were meaningless to his comprehension.

    The World Beyond

    Raymond King Cummings

  • By your figuring, we shouldn't be yet one light-year on the way.

    Out Around Rigel

    Robert H. Wilson

  • Our task was easy, because we were about half a light-year from the sun.

    Accidental Death

    Peter Baily

  • You were about right for distance, and within a few tenths of a light-year laterally.

    Skylark Three

    Edward Elmer Smith

  • The light-year is the distance that light travels in one year.

    Astronomy for Young Folks

    Isabel Martin Lewis

light-year in Science


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.