light year
UNIT OF LENGTH USED TO EXPRESS ASTRONOMICAL DISTANCES, DEFINED AS THE DISTANCE THAT LIGHT TRAVELS IN A VACUUM IN ONE YEAR
Light-years; Light-Year; Light years; Lightyears; Light-month; Light Year; Light month; Mly; Light year; Lightyear; Gigalight-year; Megalight-year; Kilolight-year
(light years)
1.
A light year is the distance that light travels in a year.
...a star system millions of light years away.
N-COUNT
2.
You can say that two things are light years apart to emphasize a very great difference or a very long distance or period of time between them. (INFORMAL)
She says the French education system is light years ahead of the English one...
N-COUNT: usu pl, N prep/adv [emphasis]