extraordinary wave

noun Radio.
  1. (of the two waves into which a radio wave is divided in the ionosphere under the influence of the earth's magnetic field) the wave with characteristics different from those that the undivided wave would have exhibited in the absence of the magnetic field.
Compare ordinary wave.

Origin of extraordinary wave

First recorded in 1880–85
Also called X-wave.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018