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light-year
noun
- Astron. a unit of distance equal to the distance that light travels in a vacuum in one year, c. 9,460,000,000,000 km (5,880,000,000,000 mi): abbrev. lt-yr or ly
- a very great distance, amount of time, etc.: usually used in pl.: light-years ahead in basic research
Also written light year
See light-year in American Heritage Dictionary 4
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