meridian (n.)

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).

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Definitions of meridian
meridian (n.)
the highest level or degree attainable; the highest stage of development;
Synonyms: acme / height / elevation / peak / pinnacle / summit / superlative / tiptop / top
meridian (n.)
an imaginary great circle on the surface of the earth passing through the north and south poles at right angles to the equator;
all points on the same meridian have the same longitude
Synonyms: line of longitude
meridian (adj.)
of or happening at noon;
meridian hour
meridian (adj.)
being at the best stage of development; "our manhood's prime vigor"- Robert Browning;
Synonyms: prime
Meridian (n.)
a town in eastern Mississippi;