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light-year

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The definition of a light-year is the unit for measuring the distance that light travels in one year, or is a long time or a great distance.

(noun)

An example of a light-year is over five trillion miles.
An example of a light-year is how far ahead one child may be in class when compared to another child; light-years ahead.

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See light-year in Webster's New World College Dictionary

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

also light year

noun

The distance that light travels in a vacuum in one year, approximately 9.46 trillion (9.46 × 10¹²) kilometers or 5.88 trillion (5.88 × 10¹²) miles.
Informal A long way. Often used in the plural: a small town light-years away from the action of the capital.

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