A lightyear is a unit of distance that is used in astronomy. It's about the distance that it takes for light to travel one year.

  • The lightyears away galaxy is very large.

  • The lightyears that it took for the signal to reach us was very long.

Definition of lightyears


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.


(only in plural) A very long way.


(only in plural) A very long time.

Nearby Words

lightyears Pronunciation in a video (3)