from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun The outermost layer of the atmosphere, between the mesosphere and interplanetary space, where air becomes extremely thin and temperatures increase steadily with altitude.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun layer of the Earth's atmosphere directly above the mesosphere and directly below the exosphere

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun the atmospheric layer between the mesosphere and the exosphere


from Wiktionary, Creative Commons Attribution/Share-Alike License

thermo- + -sphere


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