light year

noun[in the plural]3

1. •
   A 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.
2. •
   (informal, figurative) A very long way.

   • The marathon runner in the lead is light years ahead of the one at the back.
3. •
   (informal, figurative) A very long time.

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