spectra |ˈspektrə|, plural form of spectrum
spectrum |ˈspektrəm|, noun (pl. -tra |-trə|)
1 a band of colors, as seen in a rainbow, produced by separation of the components of light by their differentdegrees of refraction according to wavelength.
• ( the spectrum) the entire range of wavelengths of electromagnetic radiation.
• an image or distribution of components of any electromagnetic radiation arranged in a progressive series according to wavelength.
• a similar image or distribution of components of sound, particles, etc., arranged according to such characteristics as frequency, charge, and energy.
2 used to classify something, or suggest that it can be classified, in terms of its position on a scale between two extreme or opposite points : the left or the right of the political spectrum.
• a wide range : self-help books are covering a broader and broader spectrum.
ORIGIN early 17th cent. (in the sense [specter] ): from Latin, literally ‘image, apparition,’ from specere ‘to look.’