meridian
Noun
1
a(1)
: a great circle on the surface of the earth passing through the poles
(2)
: the half of such a circle included between the poles
b
: a representation of such a circle or half circle numbered for longitude (see LONGITUDE sense 1) on a map or globe see longitude illustration
2
: a great circle of the celestial sphere passing through its poles and the zenith of a given place see azimuth illustration
3
: any of the pathways along which the body's vital energy flows according to the theory behind acupuncture
4
: a high point (as of development or prosperity)
the problem of the unmarried don after he had passed the meridian—H. J. Laski
5
archaic : the hour of noon : MIDDAY
Source