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 galaxy in question is NGC 941, located around 55 million light-years away from Earth in the constellation Cetus. —Robert Lea, Space.com, 3 Mar. 2026

The image captures an area more than 650 light-years across in what is known as the central molecular zone (CMZ). —Claire Cameron, Scientific American, 26 Feb. 2026

For the first time, the cold gas—the raw material from which stars form—of the 650-light-year-wide region known as the Central Molecular Zone (CMZ) has been documented in unprecedented detail thanks to a giant telescope. —Michele Laufik, Martha Stewart, 26 Feb. 2026

This galaxy, located about 300 million light-years away, is practically invisible. —Jorge Garay, Wired News, 20 Feb. 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