Why is the ninth month called September?
1610s, "apparition, specter," from Latin spectrum "appearance, image, apparition," from specere "to look at, view" (see scope (n.1)). Meaning "band of colors formed from a beam of light" first recorded 1670s.
spectrum spec·trum (spěk'trəm)
n. pl. spec·trums or spec·tra (-trə)
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.
The color image presented when white light is resolved into its constituent colors: red, orange, yellow, green, blue, indigo, violet.
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.
The distribution of atomic or subatomic particles in a system, as in a magnetically resolved molecular beam, arranged in order of masses.
The group of pathogenic organisms against which an antibiotic or other antibacterial agent is effective.
Plural spectra (spěk'trə) or spectrums