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 of light-year

• 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

Located around 29,000 light-years from Earth, NGC 6723 is thought to contain some of the oldest stars in the Milky Way. — Robert Lea, Space.com, 17 July 2026

But a study in Wednesday’s issue of Nature describes observations of helium being lost from the atmosphere of an exoplanet orbiting the star LHS 1140, about 50 light-years away. — John Timmer, ArsTechnica, 16 July 2026

The exoplanet — so called because its a planet outside of our solar system — is named LhS 1140 b and is located about 49 light-years from Earth (300 trillion miles) in the constellation Cetus (the Whale). — Doyle Rice, USA Today, 16 July 2026

In this case, the Nature paper argued that, at multibillion-light-year scales, the universe’s contents weren’t spread out as uniformly as scientists had thought. — Joseph Howlett, Scientific American, 9 July 2026

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