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 planet in question, L 98-59 d, sits roughly 35 light-years away. —Mrigakshi Dixit, Interesting Engineering, 16 Mar. 2026

The picture released Wednesday by the European Southern Observatory zeroes in on a region of cold cosmic gases more than 650 light-years across. —Marcia Dunn, Los Angeles Times, 16 Mar. 2026

The researchers dug up 6,594 solar twins within roughly 1,000 light-years of Earth. —Jacek Krywko, Scientific American, 12 Mar. 2026

What the team noticed was that this supernova, which occurred around 1 billion light-years from Earth, didn't gradually fade after like a typical supernova. —Robert Lea, Space.com, 12 Mar. 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