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

Scientists have previously speculated that a GRB would vaporize anything caught in its death rays up to 200 light-years from the source. — Robin George Andrews, Scientific American, 20 Oct. 2026

Found about 37 million light-years from Earth, this galaxy sparkles in this side-on view. — Chelsea Gohd, Space.com, 20 Oct. 2026

Ellen is also the principal of Sonny’s high school, and a warm-but-firm educator naturally evokes Tami Taylor, even if Oregon is thousands of miles and metaphorical light-years away from West Texas. — Alison Herman, Variety, 20 Oct. 2026

This star is about 7,232 degrees Fahrenheit (4,000 degrees Celsius) and around 284 light-years away from Earth. — Laura Baisas, Popular Science, 15 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