The Collaborative International Dictionary
Light-year \Light-year\, Light year \Light year\ (Astron.)
The distance over which light can travel in a year's time in a vacuum, 5.88 trillion miles (9.46 trillion kilometers); -- used as a unit in expressing stellar distances. It is more than 63,000 times as great as the distance from the earth to the sun. The star nearest to the earth's sun is about 4 light years distant.
a very large difference; -- used figuratively to express great differences (of distance, quality, time) in comparisons. ``Although having the same rank and salary, they were light-years apart in their ability to perform their jobs.''
Douglas Harper's Etymology Dictionary
Wiktionary
alt. (context astronomy English) A unit of length (''abbreviation'' ly; equal to just under 10 trillion kilometres (1016 metres)) equal to the distance light travels in one Julian year; used to measure extremely large distances. n. (context astronomy English) A unit of length (''abbreviation'' ly; equal to just under 10 trillion kilometres (1016 metres)) equal to the distance light travels in one Julian year; used to measure extremely large distances.
WordNet
n. the distance that light travels in a vacuum in 1 year; 5.88 trillion miles or 9.46 trillion kilometers
Wikipedia
A light year is the distance that light travels through a vacuum in one year.
Light year(s) and lightyear(s) may also refer to:
Usage examples of "light year".
The two Earth ships and the berserkers were half a light year from the nearest sun.
The path Defiant guarded sprang from a red dwarf star four-tenths of a light year distant.