Words related to *leuk-
mid-15c., "lamp, light-giver, source of light," from Old French luminarie (12c.), "lamp, lights, lighting; candles; brightness, illumination," from Late Latin luminare "light, torch, lamp, heavenly body," literally "that which gives light," from Latin lumen (genitive luminis) "light, source of light, daylight, the light of the eye; distinguished person, ornament, glory," related to lucere "to shine," from suffixed (iterative) form of PIE root *leuk- "light, brightness."
From late 15c. as "celestial body." Sense of "notable person" is first recorded 1690s, though the Middle English word also had a figurative sense of "source of spiritual light, example of holiness" (mid-15c.). As an adjective, "pertaining to light," from 1794 but this is rare.
"to light up, illuminate," 1620s (obsolete), from *luminatus, past participle of Late Latin luminare "to shine," from Latin lumen (genitive luminis) "light," from suffixed form of PIE root *leuk- "light, brightness." Illuminate now does the job. An older verb was lumine (late 14c.); a newer one is luminize (1958). Related: Luminated; luminating; lumination; luminator.
Fluorescence and Phosphorescence — Prof. E. Wiedmann has made a new study of these phenomena. He proposes the general name luminescence for evolutions of light which do not depend on the temperature of the substance concerned. ["Photographic News," April 20, 1888]
The verb luminesce (1896) is a back-formation.
late 14c. "the moon," especially as personified in a Roman goddess answering to Greek Selene; also an alchemical name for "silver;" from Latin luna "moon, goddess of the moon," from PIE *leuksna- (source also of Old Church Slavonic luna "moon," Old Prussian lauxnos "stars," Middle Irish luan "light, moon"), suffixed form of root *leuk- "light, brightness." The luna moth (1841, American English) so called for the crescent-shaped eye-spots on its wings.
1540s, "condition of being a lunatic," formed irregularly in English from lunatic (q.v.) + -cy. Originally in reference to intermittent periods of insanity, such as were believed to be triggered by the moon's cycle. The Old English equivalent was monaðseocnes "month-sickness." In later legal use, any unsoundness of mind sufficient to render one incapable of civil transactions or management of one's affairs. Weakened figurative sense "act of madness or folly" is from 1580s.