Proto-Indo-European root meaning "light, brightness."

It forms all or part of: allumette; elucidate; illumination; illustration; lea; leukemia; leuko-; light (n.) "brightness, radiant energy;" lightning; limn; link (n.2) "torch of pitch, tow, etc.;" lucent; lucid; Lucifer; luciferase; luciferous; lucifugous; lucubrate; lucubration; luculent; lumen; Luminal; luminary; luminate; luminescence; luminous; luna; lunacy; lunar; Lunarian; lunate; lunation; lunatic; lune; lunette; luni-; luster; lustrum; lux; pellucid; sublunary; translucent.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit rocate "shines;" Armenian lois "light," lusin "moon;" Greek leukos "bright, shining, white;" Latin lucere "to shine," lux "light," lucidus "clear;" Old Church Slavonic luci "light;" Lithuanian laukas "pale;" Welsh llug "gleam, glimmer;" Old Irish loche "lightning," luchair "brightness;" Hittite lukezi "is bright;" Old English leht, leoht "light, daylight; spiritual illumination," German Licht, Gothic liuhaþ "light."

as a color, a luminous, pale bluish-green, 1590s, from sea + green (adj.). As an adjective from c. 1600. Sea-green incorruptible was Carlyle's term for Robespierre.

early 15c., "luminous, bright;" 1590s, "evident, lucid," from Latin luculentus "full of light, bright, splendid," from the stem of lux "light" (from PIE root *leuk- "light, brightness").

shining with a faint light or luminosity like that of phosphorus, luminous without sensible heat," "1766, from Modern Latin phosphorus (see phosphorus) + -escent. Related: Phosphorescently.

1660s, "orb of light, envelop of light," from photo- "light" + sphere. Astronomical sense "luminous envelop around the sun (or another star)" is from 1848. Related: Photospheric.

"a property of certain bodies of becoming luminous without undergoing combustion," 1796, from French phosphorescence (1788) or from the English verb phosphoresce "emit luminosity without combustion" (1794; see phosphorous) + -ence.