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The Collaborative International Dictionary of English v.0.48 (gcide)

Ultraviolet \Ul`tra*vi"o*let\, a. [Pref. ultra- violet.]
(Physics)
Lying outside the visible spectrum at its blue-violet end; --
said of light more refrangible (i. e. having a shorter
wavelength) than the extreme violet rays of the visible
spectrum. Electromagnetic radiation with wavelengths shorter
than those of ultrviolet light are not usually considered as
light waves, but are classified differently. The ultraviolet
region of the electromagnetic spectrum is generally
considered as comprising those electromagnetic emissions with
wavelengths lying between those of visible light and those of
X-rays, i. e. between 4000 Angstroms and 100 Angstroms.
[1913 Webster PJC]