noun an apparition; a specter.
2. spectrum ·noun the several colored and other rays of which light is composed, separated by the refraction of a prism or other means, and observed or studied either as spread out on a screen, by direct vision, by photography, or otherwise. ·see ·illust. of light, and spectroscope.
3. spectrum ·noun a luminous appearance, or an image seen after the eye has been exposed to an intense light or a strongly illuminated object. when the object is colored, the image appears of the complementary color, as a green image seen after viewing a red wafer lying on white paper. called also ocular spectrum.