Definition of light–hour
: a unit of length in astronomy that is equal to the distance that light travels in one hour in a vacuum or about 1.1 billion kilometers
Start your free trial today and get unlimited access to America's largest dictionary, with:
- More than 250,000 words that aren't in our free dictionary
- Expanded definitions, etymologies, and usage notes
- Advanced search features
- Ad free!
Seen and Heard
What made you want to look up light–hour? Please tell us where you read or heard it (including the quote, if possible).