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

The celestial phenomenon, located in a galaxy roughly 115 million light-years from Earth, is the remnant of a dense ball of stars being slowly pulled apart by the gravity of its host galaxy. — Taylor Nicioli, CNN Money, 13 Aug. 2026

These outflows, scientists say, inject an amount of energy comparable to several billion supernova explosions, driving turbulence through hot gas across distances of roughly 300,000 light-years —far beyond the boundaries of the host galaxy itself. — Sharmila Kuthunur, Space.com, 13 Aug. 2026

Sign Up for Our Free Daily Newsletter Imagine a lion with the nose of a dying star, a mane of space dust and a habitat 10,000 light-years away from Earth. — Mary Randolph, Scientific American, 12 Aug. 2026

But, as with any franchise, some of these iterations are light-years better than others. — Chris Snellgrove, Entertainment Weekly, 7 Aug. 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