Etymology
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splendor (n.)

mid-15c., splendoure, "radiance, brilliance, source of magnificence or excellence," from Old French esplendour, Anglo-French esplendour (Old French splendeur, splendor, 12c.) and directly from Latin splendor "brilliance, brightness," from splendere "be bright, shine" (see splendid).

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splendorous (adj.)
1590s, from splendor + -ous. Related: Splendorously; splendorousness.
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splendour (n.)
chiefly British English spelling of splendor; for ending see -or. Related: Splendourous; splendourously.
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splendiferous (adj.)

considered a playful elaboration since its re-birth in 1843, but in 15c. it was good English, from Medieval Latin splendorifer, from splendor (see splendor) + ferre "to bear, carry," from PIE root *bher- (1) "to carry," also "to bear children." Compare 15c. splendidious, also splendacious (1843). Bartlett (1859) offers this, allegedly from "An itinerant gospeller ... holding forth to a Kentuckian audience on the kingdom of heaven":

"Heaven, my beloved hearers," said he, "is a glorious, a beautiful, a splendiferous, an angeliferous place. Eye hath not seen, ear hath not heard, it has not entered into the imagination of any Cracker in these here diggings what carryings on the just made perfect have up thar."
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Zohar (n.)
Jewish mystical commentary on the Pentateuch, 1680s, Hebrew, literally "light, splendor."
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brightness (n.)
Old English beorhtnes "brightness, clearness, splendor, beauty;" see bright + -ness.
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royally (adv.)

late 14c., "regally, in a manner befitting a sovereign, with royal pomp and splendor;" 1836, "gloriously" (colloquial), from royal (adj.) + -ly (2).

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magnificence (n.)

mid-14c., "great-mindedness, courage," from Old French magnificence "splendor, nobility, grandeur," from Latin magnificentia "splendor, munificence," from stem of magnificus "great, elevated, noble, eminent," also "splendid, rich, fine, costly," literally "doing great deeds," from magnus "great" (from PIE root *meg- "great") + combining form of facere "to make, to do" (from PIE root *dhe- "to set, put").

Meaning "greatness of appearance or character, grandeur, glory" in English is from late 14c. That of "beauty, splendor, wealth" is 15c. As one of the Aristotelian and scholastic virtues, it translates Greek megaloprepeia "liberality of expenditure combined with good taste."

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clarity (n.)

c. 1300, clarte, clerte "brightness, radiance; glory, splendor," from Old French clerte, clartet (Modern French clarté) "clarity, brightness," from Latin claritas "brightness, splendor," also, of sounds, "clearness;" figuratively "celebrity, renown, fame," from clarare "make clear," from clarus "clear" (see clear (adj.)).

Modern form is first attested early 15c., perhaps a reborrowing directly from Latin. Original senses are obsolete; meaning "clearness" (of color, judgment, style, etc.) is from mid-15c.

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lautitious (adj.)
"sumptuous," 1640s, from Latin lautitia "elegance, splendor, magnificence," from lautus "neat, elegant, splendid," literally "washed," past participle of lavare "to wash" (from PIE root *leue- "to wash").
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