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

• 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

About 525 light-years away in the Taurus star-forming region, this young protostar is surrounded by a massive protoplanetary disk stretching 65 billion kilometers across, several times wider than our solar system. —Rupendra Brahambhatt, Interesting Engineering, 30 Aug. 2025

Astronomers have discovered a new celestial object, a compact radio beacon located in the galaxy NGS 4945, about 12 million light-years away. —New Atlas, 29 Aug. 2025

The protoplanetary disk investigated by JWST surrounds the infant star XUE 10, which is located around 5,550 light-years from Earth in the vast star-forming region known as NGC 6357. —Robert Lea, Space.com, 29 Aug. 2025

Primordial star formation Stars form when massive clouds of hydrogen many light-years across collapse under their own gravity. —ArsTechnica, 27 Aug. 2025

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