light year also light-year
1. The distance that light travels in a vacuum in one year, approximately 9.46 trillion kilometers (5.88 trillion miles).
2. often light years Informal A long way: a small town light years away from the action of the capital.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
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