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

Despite being located about 60 million light-years away in the constellation Coma Berenices, M88 is a fairly bright object in the night sky. —Adam Kovac, Scientific American, 30 May 2026

This means that the light from this ancient galaxy, which is just 1,300 light-years wide, has been travelling to Earth for just over 13 billion years. —Robert Lea, Space.com, 28 May 2026

At this speed, a journey of 10 light-years will take approximately 100 years to complete. —Kai James, The Conversation, 26 May 2026

The vast Milky Way spans about 100,000 light-years and contains anywhere between 100 billion and 400 billion stars, according to NASA. —Ashley Strickland, CNN Money, 23 May 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