light yearTranslate light year | into French | into German | into Italian | into Spanish Definition of light year noun Astronomy a unit of astronomical distance equivalent to the distance that light travels in one year, which is 9.4607 × 1012 km (nearly 6 million million miles). (light years) informal a long distance or great amount:the new range puts them light years ahead of the competitionlight year in other Oxford dictionaries Definition of light year in the US English dictionary
