/meuh rid"ee euhn/ , n.
1. Geog.
a. a great circle of the earth passing through the poles and any given point on the earth's surface.
b. the half of such a circle included between the poles.
2. Astron. the great circle of the celestial sphere that passes through its poles and the observer's zenith.
3. a point or period of highest development, greatest prosperity, or the like.
4. (in acupuncture) any of the pathways in the body along which vital energy flows.
adj.
5. of or pertaining to a meridian.
6. of or pertaining to midday or noon: the meridian hour.
7. of or indicating a period of greatest prosperity, splendor, success, etc.
[ 1350-1400; ME meridianus of noon, equiv. to meridi ( es ) midday (formed from the locative meridie at midday, by dissimilation medi die; medius MID 1 , dies day) + -anus -AN ]