From The Collaborative International Dictionary of English v.0.48:

Ultraviolet \Ul`tra*vi"o*let\, a. [Pref. ultra- + violet.]
   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]
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