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

Located about 120 light-years from Earth, the world orbits above and below the poles of its two stars, rather than along the usual flat plane. —Sharmila Kuthunur, Space.com, 26 Dec. 2025

Known as the Cosmic Christmas Tree, the cluster sits within NGC 2264, roughly 2,700 light-years from Earth. —Aamir Khollam, Interesting Engineering, 25 Dec. 2025

And depending on your preferred values for cosmic parameters, the difference might add up to just a million light-years. —Phil Plait, Scientific American, 25 Dec. 2025

In her fifth collaboration with filmmaker Yorgos Lanthimos, Emma Stone is light-years away from their childlike Poor Things creation. —Eric Andersson, PEOPLE, 20 Dec. 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