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

This is relatively close to Earth, just 444 light-years away. —ArsTechnica, 8 July 2025

One of the key things this cosmic map revealed was stars being born in vast clumps, each stretching for several thousand light-years. —Robert Lea, Space.com, 7 July 2025

In 2023, the scientists and engineers of the SMD were tasked with building the all-important Habitable Worlds Observatory, designed specifically to find alien life on planets light-years away. —Adam Frank, The Atlantic, 4 July 2025

The Milky Way is our home galaxy, a vast spiral structure with a disk of stars stretching over 100,000 light-years across. —Diana Leyva, The Tennessean, 2 July 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