light-year

US: (līt′yēr′, -yēr′)

WordReference Random House Learner's Dictionary of American English © 2025

ˈlight-ˌyear,  n. [countable]

1. Astronomy the distance that light can travel in one year, about 5.88 trillion mi. (9.46 trillion km);
   it is used as a unit in measuring distances among stars.
2. light-years, [plural]
   • a very great measure of comparison:
     Today's computers are light-years ahead of older ones in power and memory.
   • a very long time:
     Vacation already seemed light-years away.

WordReference Random House Unabridged Dictionary of American English © 2025

light-year  (līt′yēr′, -yēr′), n. 

1. Astronomy the distance traversed by light in one mean solar year, about 5.88 trillion mi. (9.46 trillion km): used as a unit in measuring stellar distances. Abbr.: lt-yr
2. light-years:
   • a very great distance, esp. in development or progress:
     The new computer is light-years ahead of the old one.
   • a very long time:
     It's been light-years since I've seen my childhood friends.

• 1885–90