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

Here, astronomers are gawking at a radio signal that appears crudely on the screen like a crooked game of Pong but turns out to be a line of data repeated every 78 seconds from 600 light-years away. —Scott Tobias, Vulture, 7 Nov. 2025

In the center is a central bulge of stars, and the whole thing is surrounded by a vast halo of stars and dark matter about a million light-years wide. —Phil Plait, Scientific American, 6 Nov. 2025

Water bodies light-years away hold volumes of water trillions of times greater than Earth’s oceans. —Kaif Shaikh, Interesting Engineering, 5 Nov. 2025

From the perspective of a stationary observer on Earth, the nearest singlet Sun-like star is Tau Ceti, about 12 light-years away. —Big Think, 5 Nov. 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