1.NounA unit of length used to measure extremely large distances, equal to approximately 9.46 trillion kilometres 10 trillion kilometres (10 metres), equivalent to the distance light travels in one Julian year.
2.NounA very long way.
"The marathon runner in the lead is light years ahead of the one at the back."
3.NounA very long time.
"Some of Leonardo da Vinci’s inventions were light years ahead of their time."