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Definition of light year noun from the Oxford Advanced American Dictionary

     

    light year

     noun
    noun
     
     
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  1. 1(astronomy) the distance that light travels in one year, about 5.88 × 1012 miles (9.4607 × 1012 kilometers) The nearest star to earth is about 4 light years away.
  2. 2light years [plural] a very long time Full employment still seems light years away.
See the Oxford Advanced Learner's Dictionary entry: light year