/ Dictionary / Index I ionosphere: Meaning and Definition of Find definitions for: i•on•o•sphere Pronunciation: (ī-on'u-sfēr"), [key] — n. the region of the earth's atmosphere between the stratosphere and the exosphere, consisting of several ionized layers and extending from about 50 to 250 mi. (80 to 400 km) above the surface of the earth. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: ionosphere (Thesaurus) ionosonde ion propulsion Related Content Daily Word Quiz: fidelity Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language