light year

plural light years · abbreviation ly · alternative lightyear · alternative light-year

1. astronomyA unit of length used to measure extremely large distances, equal to approximately 9.46 trillion kilometres 10 trillion kilometres (10¹⁶ metres), equivalent to the distance light travels in one Julian year.

   We live our lives in three dimensions for our threescore and ten allotted years. Yet every branch of contemporary science, from statistics to cosmology, alludes to processes that operate on scales outside of human experience: the millisecond and the nanometer, the eon and the light-year.

   2012 January 28, Robert L. Dorit, “Rereading Darwin”, in American Scientist, volume 100, number 1, archived from the original on 14 Nov 2012, retrieved 11 May 2013-05-11, page 23

2. figurativelyin pluralinformalA very long way.

   The marathon runner in the lead is light years ahead of the one at the back.

   1 more example

   Now that they've graduated, they'll have to make some mature decisions in their future. One of which? Settling on their signature scent that is lightyears away from the $10 body spray they had throughout school.

   2024 May 10, Hannah Oh, Daisy Maldonado, “50 College Graduation Gifts That Say, “I’m So Effing Proud of You!””, in Cosmopolitan

3. figurativelyin pluralinformalA very long time.

   Some of Leonardo da Vinci’s inventions were light years ahead of their time.