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 team suggests these blue monsters aren't galaxies at all, but are instead incredibly luminous dark stars that, because of their brightness, are being mistaken for entire galaxies with populations of stars packed into a region no wider than a few hundred light-years. —Robert Lea, Space.com, 15 Jan. 2026

The beehive is one of the closest clusters to Earth (approximately 600 light-years away) and one of the youngest (around 600 to 700 million years old). —Michele Laufik, Martha Stewart, 13 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

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