from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The portion of the atmosphere from about 30 to 80 kilometers (20 to 50 miles) above the earth's surface, characterized by temperatures that decrease from 10°C to -90°C (50°F to -130°F) with increasing altitude.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the atmospheric layer between the stratosphere and the thermosphere
meso- + -sphere (Wiktionary)