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

• galaxy
• world

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

These missions allow astronomers to study exoplanets that are millions, and even billions, of light-years away with remarkable detail by measuring small drops in starlight that happen as planets pass in front of their stars, from our perspective in the cosmos. —Victoria Corless, Space.com, 3 Apr. 2025

The collection of stars are about 34,000 light-years from Earth and estimated to be around 11 to 13 billion years old. —Hannah Poukish, Sacbee.com, 3 Apr. 2025

Astronomers look to the BAO scale, with separations of matter by about 480 million light-years, as a standard ruler. —Ashley Strickland, CNN Money, 2 Apr. 2025

This type of exoplanet is relatively rare, but 2,615 light-years away, the star named Kepler-51 is surrounded by not one but three super-puffs that are the size of Saturn but weigh only slightly more than Earth. —Shi En Kim, Smithsonian Magazine, 1 Apr. 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