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

Because of the difficulty in measuring parallaxes (distant objects' changing positions when viewed from Earth), astronomers cannot determine such distances with an accuracy of one light-year. —Joe Rao, Space.com, 27 Nov. 2025

While not visible in Hubble’s image, NGC 2775 features a hydrogen gas tail extending nearly 100,000 light-years around it. —Andrew Paul, Popular Science, 26 Nov. 2025

Eta Carinae, 7,500 light-years away, witnesses the Black Sea’s flooding. —Big Think, 24 Nov. 2025

Beta Pictoris is a young star located a little more than 60 light-years from the sun. —Phil Plait, Scientific American, 20 Nov. 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