beyond the violet in the spectrum, corresponding to light having wavelengths shorter than 4000 angstrom units.
pertaining to, producing, or utilizing light having such wavelengths: an ultraviolet lamp.
ultraviolet radiation.
Compare infrared.

1870–75; ultra- + violet

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World English Dictionary
ultraviolet (ˌʌltrəˈvaɪəlɪt)
1.  the part of the electromagnetic spectrum with wavelengths shorter than light but longer than X-rays; in the range 0.4 × 10--6 and 1 × 10--8 metres
2.  UV of, relating to, or consisting of radiation lying in the ultraviolet: ultraviolet radiation

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

"beyond the violet end of the visible spectrum," 1840, from ultra- + violet. Ultra-red (1870) was a former name for what now is called infra-red.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

ultraviolet ul·tra·vi·o·let (ŭl'trə-vī'ə-lĭt)
Abbr. UV, U.V.
Of or relating to the range of invisible radiation wavelengths from about 4 nanometers, on the border of the x-ray region, to about 380 nanometers, just beyond the violet in the visible spectrum. n.
Ultraviolet light or the ultraviolet part of the spectrum.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
ultraviolet   (ŭl'trə-vī'ə-lĭt)  Pronunciation Key 
Adjective   Relating to electromagnetic radiation having frequencies higher than those of visible light but lower than those of x-rays, approximately 1015-1016 hertz. Some animals, such as bees, are capable of seeing ultraviolet radiation invisible to the human eye. See more at electromagnetic spectrum.

Noun   Ultraviolet light or the ultraviolet part of the spectrum. See Note at infrared.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
Let deck dry for two days before applying a clear wood preservative with mildewcides and ultraviolet-light inhibitors.
Starling plumage reflects quite a lot of ultraviolet-as can be seen in photographs taken using special ultraviolet-sensitive film.
Because of that old museum curator's bugaboo: ultraviolet light.
Birds see ultraviolet markings on flowers, signs invisible to us.
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