spectrum (n.)youdaoicibaDictYouDict[spectrum 词源字典]
1610s, "apparition, specter," from Latin spectrum (plural spectra) "an appearance, image, apparition, specter," from specere "to look at, view" (see scope (n.1)). Meaning "visible band showing the successive colors, formed from a beam of light passed through a prism" first recorded 1670s. Figurative sense of "entire range (of something)" is from 1936.[spectrum etymology, spectrum origin, 英语词源]
visual (adj.)youdaoicibaDictYouDict
early 15c., "pertaining to the faculty of sight;" also "coming from the eye or sight" (as a beam of light was thought to do), from Late Latin visualis "of sight," from Latin visus "a sight, a looking; power of sight; things seen, appearance," from visus, past participle of videre "to see" (see vision). Meaning "perceptible by sight" is from late 15c; sense of "relating to vision" is first attested c. 1600. The noun meaning "photographic film or other visual display" is first recorded 1944.