spectrum (n.)youdaoicibaDictYouDict
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.
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.