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light year

 
/ˈlɑɪt ˌyɪər/ n [C] earth science

Definition

the great distance that light travels in one year; about 5,880,000,000,000 miles or 9,460,000,000,000 kilometers 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 n from the Cambridge Academic Content Dictionary © Cambridge University Press)

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