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

Biosignatures are possible signs of biology on other planets, whereas technosignatures are clues to the presence of advanced technology that might be detectable across light-years. — Keith Cooper, Space.com, 27 July 2026

The planet, known as LhS 1140 b, is about 49 light-years from Earth, or 300 trillion miles, said Collin Cherubim of Harvard University, lead author of the study reporting the discovery. — Robert Abitbol, USA Today, 25 July 2026

Such are the strange semantic questions raised by studies of CD-35 2722 B, a brown dwarf with about 30 times the mass of Jupiter that’s orbiting a small star that is some 73 light-years from Earth in the system CD-35 2722. — Adam Kovac, Scientific American, 22 July 2026

But one stellar system about 72 light-years from Earth isn’t quite like anything else researchers have ever seen. — Andrew Paul, Popular Science, 22 July 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