from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- noun a region of the ionosphere (from 50 to 90 miles up) that reflects radio waves of medium length
from The American Heritage® Dictionary of the English Language, 4th Edition
[After Edwin Kennelly, (1861–1939), American physicist, and Oliver, Heaviside, (1850–1925), British physicist.]
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