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English definition of “light year”

light year

noun [C]  /ˈlɑɪt ˌyɪər/ us  
earth science the great distance that light travels in one year; about 5,880,000,000,000 miles or 9,460,000,000,000 kilometers earth science People sometimes say light years to talk about an extremely long distance or time: When I was a young man, being 50 seemed light years away.
(Definition of light year from the Cambridge Academic Content Dictionary © Cambridge University Press)
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