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From The Collaborative International Dictionary of English v.0.48:
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]