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

This white dwarf is designated RXJ0528+2838 and is located 730 light-years away from Earth. —Robert Lea, Space.com, 12 Jan. 2026

Our nearest star system is more than four light-years away, which means even a simple question and reply could take over a decade. —Rupendra Brahambhatt, Interesting Engineering, 11 Jan. 2026

Located about 600 light-years away, the cluster is one of the closest of its kind to Earth, according to NASA. —Eric Lagatta, USA Today, 9 Jan. 2026

The two planets, roughly four times the size of Earth, were discovered to be orbiting around a millisecond pulsar star named PSR B1257+12, which is 2,300 light-years away. —Lorenzino Estrada, AZCentral.com, 9 Jan. 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