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

Moisturizer’s confidence level feels light-years away from its predecessor — and starts with their respective album artwork. —Sophie Williams, Billboard, 10 Oct. 2025

Although there are many others, these five stars are all located within a mere 12 light-years of Earth. —Ethan Siegel, Big Think, 7 Oct. 2025

So far, no direct image of 51 Pegasi b has been taken; the planet is too far away from Earth (50 light-years) and too close to its star to be seen by even our best telescopes. —Keith Cooper, Space.com, 6 Oct. 2025

The rogue planet, which does not orbit any star, is called Cha 1107-7626 and is outside of our solar system, 620 light-years from Earth in the Chamaeleon constellation. —Ashley Strickland, CNN Money, 2 Oct. 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