from The American Heritage® Dictionary of the English Language, 4th Edition
- n. An atmospheric area about 80 kilometers (50 miles) above the earth's surface, forming the upper boundary of the mesosphere.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. In the atmosphere, the boundary between the mesosphere and the ionosphere. It is the atmospheric boundary where the temperature reaches its minimum value.
Sorry, no etymologies found.