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

Triangulum Galaxy Next came the Triangulum Galaxy, M33, a spiral galaxy about 3 million light-years away from Earth in the constellation Triangulum. —Daisy Dobrijevic, Space.com, 15 May 2026

The magnifying glass The LAP1-B is 13 billion light-years away from Earth. —Jacek Krywko, ArsTechnica, 13 May 2026

The nearby universe refers to regions within about one billion light-years of Earth. —Aamir Khollam, Interesting Engineering, 12 May 2026

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