An Etymological Dictionary of Astronomy and Astrophysics

1. Geography: An imaginary line on the Earth’s surface joining the north and south poles at right angles to the equator. See also → local meridian, → prime meridian.
   

2. Astron.: An imaginary great circle on the → celestial sphere that passes through its poles
   and the observer’s → zenith.

Etymology (EN): M.E., from O.Fr. meridien, from L. meridianus “of noon, southern,” from meridies “noon, south,” from meridie “at noon,” altered by dissimilation from *medi die, locative of medius “mid-” + dies “day.”

Etymology (PE): Nimruzân, coined by Pers. astronomer (A.D. 973-1048) in his at-Tafhim, from nim “mid-, half” (Mid.Pers. nêm, nêmag “half;” Av. naēma- “half;” cf. Skt. néma- “half”)

• ruz, → day, + -ân suffix denoting time and place.