light–year 
/ˈlaɪtˌjiɚ/ noun
plural light–years /ˈlaɪtˌjiɚ/ noun 1 [count] technical : a unit of distance equal to the distance that light travels in one year (about 5.88 trillion miles or 9.46 trillion kilometers)
▪ a star about 10 light-years away 2 light-years [plural] a — used to say that someone or something is much better or more advanced than others ▪ This new technology puts the company light-years ahead [=very far ahead] of its competitors.
b — used to refer to a time that is or seems very far away ▪ A cure for that disease is still probably light-years away.
▪ a star about 10 light-years away
b — used to refer to a time that is or seems very far away ▪ A cure for that disease is still probably light-years away.
