T0159800 (thûr′mə-sfîr′)n. The outermost layer of the atmosphere, between the mesosphere and interplanetary space, where air becomes extremely thin and temperatures increase steadily with altitude.ther′mo·spher′ic(-sfîr′ĭk, -sfĕr′ĭk) adj.
thermospheric
(ˌθɜːməʊˈsfɛrɪk) adj (Physical Geography) pertaining to the thermosphereEncyclopediaSeethermosphere