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

Aldebaran is the fourteenth brightest star in the sky and lies 67 light-years from Earth. — Joe Rao, Space.com, 10 July 2026

In this case, the Nature paper argued that, at multibillion-light-year scales, the universe’s contents weren’t spread out as uniformly as scientists had thought. — Joseph Howlett, Scientific American, 9 July 2026

Rubin released its first images last year, including colorful shots of the Trifid and Lagoon nebulas located thousands of light-years from Earth. — Adithi Ramakrishnan, Los Angeles Times, 7 July 2026

And like the photons that travel billions of light-years to reach us, new fragments are constantly falling into place. — Quanta Magazine, 2 July 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