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The visible spectrum
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From Latin spectrum (appearance, image, apparition), from speciō (look at, view). Doublet of specter. See also scope.


  • (Canada, UK) IPA(key): /ˈspektɹəm/
  • (file)
  • (US) IPA(key): /ˈspɛkt͡ʃɹəm/
    • (file)
  • Rhymes: -ɛktɹəm


spectrum (plural spectra or spectrums)

  1. A range; a continuous, infinite, one-dimensional set, possibly bounded by extremes.
    • 2012 November 7, Matt Bai, “Winning a Second Term, Obama Will Confront Familiar Headwinds”, in New York Times[1]:
      As Mr. Obama prepared to take the oath, his approval rating touched a remarkable 70 percent in some polling — a reflection of good will across the political spectrum.
  2. Specifically, a range of colours representing light (electromagnetic radiation) of contiguous frequencies; hence electromagnetic spectrum, visible spectrum, ultraviolet spectrum, etc. [from later 17th c.]
    • 2010 October 30, Jim Giles, “Jammed!”, in New Scientist:
      Current 3G technologies can send roughly 1 bit of data - a one or a zero - per second over each 1 Hz of spectrum that the operator owns.
  3. (psychology, education, usually with the) The autism spectrum.
    • 2022, Percival Everett, Dr. No, Influx Press (2023), page 110:
      He punctuated his words with a look into my eyes that might have been read as threatening or menacing by anyone who was not on the spectrum. But I am on the spectrum, and so I stared back at him.
  4. (chemistry) The pattern of absorption or emission of radiation produced by a substance when subjected to energy (radiation, heat, electricity, etc.).
  5. (mathematics, linear algebra) The set of eigenvalues of a matrix.
    Synonym: eigenspectrum
  6. (mathematics, functional analysis) Of a bounded linear operator A, the set of scalar values λ such that the operator A—λI, where I denotes the identity operator, does not have a bounded inverse; intended as a generalisation of the linear algebra sense.
  7. (abstract algebra, algebraic geometry) The set, denoted Spec(R), of all prime ideals of a given ring R, commonly augmented with a Zariski topology and considered as a topological space.
    Hyponym: Stone space
  8. (obsolete) Specter, apparition. [from early 17th c.]
  9. The image of something seen that persists after the eyes are closed.

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The translations below need to be checked and inserted above into the appropriate translation tables. See instructions at Wiktionary:Entry layout § Translations.



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From Latin spectrum (appearance, image, apparition), from speciō (look at, view).



spectrum n (plural spectrums or spectra, diminutive spectrumpje n)

  1. spectrum

Derived terms[edit]



From spec(iō) (look at, behold) +‎ -trum (making it a doublet of speculum).

The only attestation in Classical antiquity is in a pair of letters between Cicero and Cassius Longinus which imply that the Epicurean Catius (fl. c. 50s–40s BC) used spectrum as a translation of the Greek philosophical term εἴδωλον (eídōlon, image).[1] It may therefore have been coined by Catius as a neologism, although alternatively, it could be an undocumented but preexisting word that he repurposed as a technical term.

After Cicero, the word is extremely sparsely attested until being revived around the start of the sixteenth century by Renaissance humanist authors with the meaning "apparition" or "phantom", possibly influenced by the fact that Greek εἴδωλον also had this sense.[2]

The scientific use to refer to the visible spectrum of colored light was first introduced by Isaac Newton, who used the word in the second half of the seventeenth century in both his English writings and in his first Latin draft of the Opticks, the Fundamentum Opticae, although the 1706 Latin translation of Opticks by Samuel Clarke translates Newton's English spectrum into Latin as imago.[3]



spectrum n (genitive spectrī); second declension

  1. appearance, image
    • 62 BCE – 43 BCE, Cicero, Epistulae ad Familiares 15.16.1–2:
      fit enim nescio qui ut quasi coram adesse videare cum scribo aliquid ad te, neque id κατ’ εἰδ<ώλ>ων φαντασίας, ut dicunt tui amici novi, qui putant etiam διανοητικὰς φαντασίας spectris Catianis excitari. nam, ne te fugiat, Catius Insuber Ἐπικούρειος, qui nuper est mortuus, quae ille Gargettius et iam ante Democritus εἴδωλα, hic spectra nominat. his autem spectris etiam si oculi possent feriri, quod <pup>ulis ipsa incurrunt, animus qui possit ego non video; doceas tu me oportebit cum salvus veneris. in meane potestate ut sit spectrum tuum, ut, simul ac mihi collibitum sit de te cogitare, illud occurrat? neque solum de te, qui mihi haeres in medullis, sed si insulam Britanniam coepero cogitare, eius εἴδωλον mihi advolabit ad pectus?
      • 1900 translation by Evelyn Shuckburgh[4]
        For somehow it makes you seem almost present when I write anything to you, and that not 'by way of phantoms of images,' as your new friends express it, who hold that 'mental pictures' are caused by what Catius called 'spectres' — for I must remind you that Catius Insuber the Epicurean, lately dead, calls 'spectres' what the famous Gargettius, and before him Democritus, used to call 'images.' Well, even if my eyes were capable of being struck by these 'spectres,' because they spontaneously run in upon them at your will, I do not see how the mind can be struck. You will be obliged to explain it to me, when you return safe and sound, whether the 'spectre' of you is at my command, so as to occur to me as soon as I have taken the fancy to think about you; and not only about you, who are in my heart's core, but supposing I begin thinking about the island of Britain — will its image fly at once into my mind?
  2. apparition, specter, phantom
    • 1524, Desiderius Erasmus, Exorcismus sive spectrum :
      Iam pridem vagabatur rumor ac fabula per eius loci rusticos, iuxta ponticulum hunc observari spectrum quoddam, cuius subinde exaudirentur miserandi eiulatus: suspicabantur, animam esse cuiuspiam, quae diris cruciatibus torqueretur.
  3. (New Latin) spectrum (band of light arranged in order by wavelength)
    • c. 1687-88, Isaac Newton, Fundamentum Opticae[5] :
      Considerabam praeterea quod latitudine foraminis F per quod lux in cubiculum ingreditur fit penumbra in circuitu spectri Y, et penumbra illa permanet in lateribus rectilineis spectrorum PT et pt.
      • Translation by Alan E. Shapiro
        I further considered that by the breadth of the hole F, through which the light enters the room, a penumbra is made in the border of the spectrum Y, and that penumbra remains in the straight sides of the spectra PT and pt.


Second-declension noun (neuter).

Case Singular Plural
Nominative spectrum spectra
Genitive spectrī spectrōrum
Dative spectrō spectrīs
Accusative spectrum spectra
Ablative spectrō spectrīs
Vocative spectrum spectra


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  1. ^ "Why is Latin spectrum a Bad Translation of Epicurus’ ΕΙΔΩΛΟΝ?", Sean McConnell, 2018. Mnemosyne 72 (2019) 154-162.
  2. ^ "Spectrum : Probleme einer Wortgeschichte, vom Altertum zur Neuzeit", Mario Puelma, 1985. Museum Helveticum Vol. 42, No. 2. page 230
  3. ^ Newton’s Sensorium: Anatomy of a Concept, Jamie C. Kassler, 2018, page 4
  4. ^ Evelyn Shuckburgh, Cicero: The Whole Extant Correspondence in Chronological Order (London 1900)
  5. ^ The Optical Papers of Isaac Newton, Vol. II. Edited Alan E. Shapiro, 2021. Pages 258-259.

Further reading[edit]

  • spectrum”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
  • spectrum”, in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
  • spectrum in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
  • spectrum in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette