spec·trum

[spek-truhm]
noun, plural spec·tra [-truh] , spec·trums.
1.
Physics.
a.
an array of entities, as light waves or particles, ordered in accordance with the magnitudes of a common physical property, as wavelength or mass: often the band of colors produced when sunlight is passed through a prism, comprising red, orange, yellow, green, blue, indigo, and violet.
b.
this band or series of colors together with extensions at the ends that are not visible to the eye, but that can be studied by means of photography, heat effects, etc., and that are produced by the dispersion of radiant energy other than ordinary light rays. Compare band spectrum, electromagnetic spectrum, mass spectrum.
2.
a broad range of varied but related ideas or objects, the individual features of which tend to overlap so as to form a continuous series or sequence: the spectrum of political beliefs.
Origin:
1605–15; < Latin: appearance, form, equivalent to spec(ere) to look, regard + -trum instrumental noun suffix

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Based on the Random House Dictionary, © Random House, Inc. 2013.
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Collins
World English Dictionary
spectrum (ˈspɛktrəm) [Click for IPA pronunciation guide]
 
—n , pl -tra
1.  the distribution of colours produced when white light is dispersed by a prism or diffraction grating. There is a continuous change in wavelength from red, the longest wavelength, to violet, the shortest. Seven colours are usually distinguished: violet, indigo, blue, green, yellow, orange, and red
2.  the whole range of electromagnetic radiation with respect to its wavelength or frequency
3.  absorption spectrum See also emission spectrum any particular distribution of electromagnetic radiation often showing lines or bands characteristic of the substance emitting the radiation or absorbing it
4.  any similar distribution or record of the energies, velocities, masses, etc, of atoms, ions, electrons, etc: a mass spectrum
5.  any range or scale, as of capabilities, emotions, or moods
6.  another name for an afterimage
 
[C17: from Latin: appearance, image, from spectāre to observe, from specere to look at]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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00:10
Spectrum is always a great word to know.
So is doohickey. Does it mean:
a screen or mat covered with a dark material for shielding a camera lens from excess light or glare.
a gadget; dingus; thingumbob.
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Etymonline
Word Origin & History

spectrum
1611, "apparition, specter," from L. spectrum "appearance, image, apparition," from specere "to look at, view" (see scope (1)). Meaning "band of colors formed from a beam of light" first recorded 1671. Spectroscope (1861) is a hybrid, with Gk. -skopion, from skopein "to look
at, examine," which is from the same PIE root as spectrum.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

spectrum spec·trum (spěk'trəm)
n. pl. spec·trums or spec·tra (-trə)

  1. The distribution of a characteristic of a physical system or phenomenon, especially the distribution of energy emitted by a radiant source arranged in order of wavelengths.

  2. The color image presented when white light is resolved into its constituent colors: red, orange, yellow, green, blue, indigo, violet.

  3. The plot of intensity as opposed to wavelength of light emitted or absorbed by a substance, usually characteristic of the substance and used in qualitative and quantitative analysis.

  4. The distribution of atomic or subatomic particles in a system, as in a magnetically resolved molecular beam, arranged in order of masses.

  5. The group of pathogenic organisms against which an antibiotic or other antibacterial agent is effective.

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
spectrum   (spěk'trəm)  Pronunciation Key 
Plural spectra (spěk'trə) or spectrums

  1. A range over which some measurable property of a physical phenomenon, such as the frequency of sound or electromagnetic radiation, or the mass of specific kinds of particles, can vary. For example, the spectrum of visible light is the range of electromagnetic radiation with frequencies between between 4.7 × 1014 and 7.5 × 1014 hertz.

  2. The observed distribution of a phenomenon across a range of measurement. See more at atomic spectrum, spectroscopy.


The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary

spectrum definition


The range of wavelengths characteristic of a specific type of radiation.

Note: The spectrum making up visible light contains light in the colors violet, indigo, blue, green, yellow, orange, and red, with violet having the shortest wavelength and highest frequency, and red having the longest wavelength and lowest frequency.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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FOLDOC
Computing Dictionary

Spectrum definition


ZX Spectrum

The Free On-line Dictionary of Computing, © Denis Howe 2010 http://foldoc.org
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Example sentences
At the other end of the spectrum are vast, open-pit mines run by the world's
  largest mining companies.
Merwin's nonpunctuation is one extreme choice from a wide spectrum of
  possibility.
Bosses bemoaned the downturn and demanded free radio spectrum to stimulate the
  industry.
Air pollution can trigger or worsen a wide spectrum of respiratory and
  cardiovascular ailments.
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