meridian

An imaginary great circle on the earth’s surface passing through the North and South geographic poles.

Either half of such a great circle from pole to pole. All points on the same meridian have the same longitude.

A great circle passing through the two poles of the celestial sphere and the zenith of a given observer.

A curve on a surface of revolution, formed by the intersection of the surface with a plane containing the axis of revolution.

A plane section of a surface of revolution containing the axis of revolution.

Any of the longitudinal lines or pathways on the body along which the acupuncture points are distributed.

The highest point in the sky reached by the sun or another celestial body; a zenith.