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 feature, nicknamed the Cat's Tail, extends out from the debris disk known as Beta Pictoris which is located in a planetary system located 63 light-years away. — Robert Lea, Space.com, 3 Nov. 2026

While the damage was minor, this was all caused by the magnetar SGR 1806-20, which is 50,000 light-years away, halfway across our galaxy. — Phil Plait, Scientific American, 30 Oct. 2026

In 2024, a separate team used these tools to create a continuous three-dimensional map of the density of the ISM’s dust inside a sphere more than 4,000 light-years wide around our sun. — Perri Thaler, Quanta Magazine, 30 Oct. 2026

According to Fuller, neutrinos can even travel through light-years of lead without stopping, depending on their energy. — Georgina Jedikovska, Interesting Engineering, 23 Oct. 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