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 vast Milky Way spans about 100,000 light-years and contains anywhere between 100 billion and 400 billion stars, according to NASA. —Ashley Strickland, CNN Money, 23 May 2026

The image captures the Crystal Ball Nebula, or NGC 1514, a planetary nebula found some 1,500 light-years away from us in the constellation Taurus, the Bull. —Brett Tingley, Space.com, 22 May 2026

But the far side of the Milky Way’s disk would be twice that distance from Andromeda, well more than 200,000 light-years. —Phil Plait, Scientific American, 22 May 2026

Just to the left of the lion’s tail is a cluster of distant galaxies around 60 million light-years away. —Mike Lynch, Twin Cities, 10 May 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