[me.rid.i.an] n [ME, fr. MF meridien, fr. meridien of noon, fr. L meridianus, fr. meridies noon, south, irreg. fr. medius mid + dies day--more at mid, deity] (14c) 1 archaic: the hour of noon: midday
2: a great circle of the celestial sphere passing through its poles and the zenith of a given place
3: a high point
4. 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 on a map or globe--see longitude illustration -- meridian adj