1 the band of colours, as seen in a rainbow etc., arranged in a progressive series according to their refrangibility or wavelength.
2 the entire range of wavelengths of electromagnetic radiation.
3 a an image or distribution of parts of electromagnetic radiation arranged in a progressive series according to wavelength. b this as characteristic of a body or substance when emitting or absorbing radiation.
4 a similar image or distribution of energy, mass, etc., arranged according to frequency, charge, etc.
5 the entire range or a wide range of anything arranged by degree or quality etc.
6 (in full ocular spectrum) an after-image.
Phrases and idioms:
spectrum (or spectral) analysis chemical analysis by means of a spectroscope.
Etymology: L, = image, apparition f. specere look
Useful english dictionary. 2012.