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

Looking beyond the main structure captured by Webb, the galaxy’s spiral arms extend into a faint, wide ring of hydrogen gas stretching thousands of light-years. —Bojan Stojkovski, Interesting Engineering, 10 May 2026

Its anchor, Arcturus, is 37 light-years distant and a red giant star — its color leading Chinese astronomers to see it as a horn of a giant dragon. —Jamie Carter, Space.com, 8 May 2026

These shards travel billions of light-years across the universe and slam into Earth’s atmosphere. —Quanta Magazine, 6 May 2026

From within our own galaxy to behemoths billions of light-years away, supermassive black holes create jets like nothing else in the cosmos. —Big Think, 4 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