mid-14c., "noon, midday," from Old French meridien "of the noon time, midday; the meridian; a southerner" (12c.), and directly from Latin meridianus "of midday, of noon, southerly, to the south," from meridies "noon, south," from meridie "at noon," altered by dissimilation from pre-Latin *medi die, locative of medius "mid-" (from PIE root *medhyo- "middle") + dies "day" (from PIE root *dyeu- "to shine").
The cartographic sense of "a great circle or half-circle of a sphere passing through the poles" is attested from late 14c., originally astronomical. Figurative uses tend to suggest "point of highest development or fullest power," implying a subsequent decline. As an adjective from late 14c. Related: Meridional. The city in Mississippi, U.S., was settled 1854 (as Sowashee Station) at a railway junction and given its current name in 1860, supposedly by people who thought meridian meant "junction" (they perhaps confused the word with median).
"southern France," 1883, from French midi "south," literally "midday" (12c.), from mi "middle" (from Latin medius "middle;" see medial (adj.)) + di "day" (from Latin dies, from PIE root *dyeu- "to shine"). At midday in the northern hemisphere the sun is in the south of the sky. Compare Latin meridianus "of midday, of noon;" also "southerly, to the south" (see meridian), and Middle English mid-dai in its secondary sense "south, to the south" (late 14c.).
It forms all or part of: amid; intermediate; mean (adj.2) "occupying a middle or intermediate place;" medal; medial; median; mediate; medieval; mediocre; Mediterranean; medium; meridian; mesic; mesial; meso-; meson; Mesopotamia; Mesozoic; mezzanine; mezzo; mezzotint; mid (prep., adj.); middle; Midgard; midriff; midst; midwife; milieu; minge; mizzen; moiety; mullion.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit madhyah, Avestan madiya- "middle," Greek mesos, Latin medius "in the middle, between; from the middle," Gothic midjis, Old English midd "middle," Old Church Slavonic medzu "between," Armenian mej "middle."
Proto-Indo-European root meaning "to shine," in derivatives "sky, heaven, god."
It forms all or part of: adieu; adios; adjourn; Asmodeus; circadian; deific; deify; deism; deity; deodand; deus ex machina; deva; dial; diary; Diana; Dianthus; diet (n.2) "assembly;" Dioscuri; Dis; dismal; diurnal; diva; Dives; divine; joss; journal; journalist; journey; Jove; jovial; Julia; Julius; July; Jupiter; meridian; Midi; per diem; psychedelic; quotidian; sojourn; Tuesday; Zeus.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit deva "god" (literally "shining one"); diva "by day;" Avestan dava- "spirit, demon;" Greek delos "clear;" Latin dies "day," deus "god;" Welsh diw, Breton deiz "day;" Armenian tiw "day;" Lithuanian dievas "god," diena "day;" Old Church Slavonic dini, Polish dzień, Russian den "day;" Old Norse tivar "gods;" Old English Tig, genitive Tiwes, name of a god.
also siderial, 1630s, "star-like;" 1640s, "of or pertaining to the stars," earlier sideral (1590s), from French sidereal (16c.), from Latin sidereus "starry, astral, of the constellations," from sidus (genitive sideris) "star, group of stars, constellation," which is of uncertain origin, perhaps from PIE root *sweid- "to shine" (source also of Lithuanian svidus "shining, bright").
Sidereal time is measured by the apparent diurnal motion of the fixed stars. The sidereal day begins and ends with the passage of the vernal equinox over the meridian and is about four minutes shorter than the solar day, measured by the passage of the sun over the meridian.
late 14c., "first, original, first in order of time," from Old French prime and directly from Latin primus "first, the first, first part," figuratively "chief, principal; excellent, distinguished, noble" (source also of Italian and Spanish primo), from Proto-Italic *prismos, superlative of PIE *preis- "before," from root *per- (1) "forward," hence "in front of, before, first, chief."
The meaning "of fine quality, of the first excellence" is from c. 1400. The meaning "first in rank, degree, or importance" is from 1610s in English. Arithmetical sense (as in prime number, one indivisible without a remainder except by 1) is from 1560s; prime meridian "the meridian of the earth from which longitude is measured, that of Greenwich, England," is from 1878. Prime time originally (c. 1500) meant "spring time;" the broadcasting sense of "peak tuning-in period" is attested by 1961.