light-year

noun

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. Abbreviation: lt-yr
2. light-years,
   1. a very great distance, especially in development or progress: The new computer is light-years ahead of the old one.
   2. a very long time: It’s been light-years since I’ve seen my childhood friends.

1. The distance that light travels in a vacuum in one year, equal to about 9.46 trillion km (5.88 trillion mi). Light-years are used in measuring interstellar and intergalactic distances. Compare astronomical unit parsec.