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, known as Elias 2-24 b, is roughly the mass of Jupiter and sits about 450 light-years from Earth, according to NASA. — Paloma Chavez, PEOPLE, 25 Sep. 2026

This revealed a 100 light-year-wide bubble where the jet strikes interstellar gas and dust. — Robert Lea, Space.com, 24 Sep. 2026

These candidates include TRAPPIST-1e, a planet located about 40 light-years from Earth widely regarded as one of the most promising locations for alien life. — Andrew Paul, Popular Science, 23 Sep. 2026

Others are top-of-the-line machines, pointed at distant galaxies millions of light-years away. — Sean MacAday, Sacbee.com, 19 Sep. 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