An Etymological Dictionary of Astronomy and Astrophysics
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Tending to → vanish gradually.

Verbal adj. from → evanesce.

A wave whose → amplitude → decreases → exponentially with distance from the → interface at which it is formed. Evanescent waves are formed when → sinusoidal waves are internally reflected off an interface at an angle greater than the → critical angle so that → total internal reflection occurs.

→ evanescent; → wave.