demi-monde n.

word-forming element meaning "half, half-sized, partial," used in English from mid-14c., especially in technical terms from French, from Old French demi "half" (12c.), from Late Latin dimedius, from Latin dimidius "half, one-half," which contains the elements dis- "apart" (see dis-) + medius "in the middle, between; from the middle," as a noun "the middle;" from PIE root *medhyo- "middle." Formerly also demy-, and in early use often written as a separate word.

mid-15c., mondeine, "of this world, worldly, terrestrial," from Old French mondain "of this world, worldly, earthly, secular;" also "pure, clean; noble, generous" (12c.) and directly from Late Latin mundanus "belonging to the world" (as distinct from the Church), in classical Latin "a citizen of the world, cosmopolite," from mundus "universe, world," which is identical to mundus  "clean, elegant," but the exact connection is uncertain and the etymology is unknown.

Latin mundus "world" was used as a translation of Greek kosmos (see cosmos) in its Pythagorean sense of "the physical universe" (the original sense of the Greek word was "orderly arrangement"). Like kosmos (and perhaps by influence of it), Latin mundus also was used of a woman's "ornaments, dress," which also could entangle the adjective mundus "clean, elegant."

The English word's extended sense of "dull, uninteresting" is attested by 1850. Related: Mundanely. The mundane era was the chronology that began with the supposed epoch of the Creation (famously reckoned as 4004 B.C.E.).

mid-14c., reputacioun, "credit, good reputation, esteem;" late 14c. in the general sense of "opinion, estimation," good or bad; from Old French reputation, reputacion, and directly from Latin reputationem (nominative reputatio) "a reckoning, consideration, a thinking over," noun of action from past-participle stem of reputare "reflect upon, reckon, count over."

This is from re-, here perhaps "repeatedly" (see re-), + putare "to judge, suppose, believe, suspect," originally "to clean, trim, prune" (from PIE root *pau- (2) "to cut, strike, stamp").