Webster's Revised Unabridged Dictionary · 1913

Meridian

Meridian , a.

[F. méridien, L. meridianus pertaining to noon, fr. meridies noon, midday, for older medidies; medius mid, middle + dies day. See Mid, and Diurnal.]

1.
Being at, or pertaining to, midday; belonging to, or passing through, the highest point attained by the sun in his diurnal course.
Tables... to find the altitude meridian. — Chaucer
2.
Pertaining to the highest point or culmination; as, meridian splendor.

Meridian , n.

[F. méridien. See Meridian, a.]

1.
Midday; noon.
2.
Hence: The highest point, as of success, prosperity, or the like; culmination.
I have touched the highest point of all my greatness,b And from that full meridian of my gloryb I haste now to my setting. — Shakespeare
3.
A great circle of the sphere passing through the poles of the heavens and the zenith of a given place. It is crossed by the sun at midday.
4.
A great circle on the surface of the earth, passing through the poles and any given place; also, the half of such a circle included between the poles.
All other knowledge merely serves the concerns of this life, and is fitted to the meridian thereof. — Sir M. Hale