from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The outermost region of a planet's atmosphere.
- n. The outermost layer of the earth's atmosphere, lying above the thermosphere and extending thousands of kilometers into space, from which molecules having sufficient velocity can escape the earth's gravitation.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. the uppermost layer of a planet's atmosphere
- n. an extremely thin atmosphere, as on Saturn's moon Dione
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the outermost atmospheric layer
Sorry, no etymologies found.