light-year

noun

ˈlīt-ˌyir 

1

: a unit of length in astronomy equal to the distance that light travels in one year in a vacuum or about 5.88 trillion miles (9.46 trillion kilometers)

2

: an extremely large measure of comparison (as of distance, time, or quality)

seems like light-years ago

has light-years more talent

two minutes and yet light-years away from the crowded village

—Suzanne Patterson

Synonyms

• world
• galaxy

Examples of light-year in a Sentence

my sister and I are close in age, but personality-wise, there are light-years between us

Recent Examples on the Web

An open cluster of stars about 445 light-years from the solar system, the Pleiades looks fabulous with the naked eye. —Jamie Carter, Forbes.com, 14 Aug. 2025

Located in a galaxy with little ongoing star formation about 730 million light-years away, it was detected by a new artificial intelligence (AI) system built to flag unusual cosmic events in real time. —Sharmila Kuthunur, Space.com, 13 Aug. 2025

Like Einstein, Brassard feels repulsed by the way the particles in the Bell experiment seem to have firsthand awareness of each other despite being separated by, in principle, light-years of space. —Quanta Magazine, 8 Aug. 2025

Careful measurement of the expanding light echo was used to determine V838’s distance from us, about 20,000 light-years. —Phil Plait, Scientific American, 7 Aug. 2025

Word History

First Known Use

1864, in the meaning defined at sense 1

Rhymes for light-year

• atmosphere
• biosphere
• centromere
• chemosphere
• chromosphere
• hemisphere
• hydrosphere
• lithosphere
• mesosphere
• microsphere
• miserere
• mountaineer

Kids Definition

light-year

noun

ˈlīt-ˌyi(ə)r

1

: a unit of length in astronomy equal to the distance that light travels in one year or 5,880,000,000,000 miles (9,460,000,000,000 kilometers)

2

: a very great distance especially in progress

light-years ahead in design