Being at, or pertaining to, midday; belonging to, or passing through, the highest point attained by the sun in his diurnal course.
- An imaginary great circle on the earth's surface passing through the North and South geographic poles. All points on the same meridian have the same longitude.
- Either half of such a great circle from pole to pole.
- Astronomy A great circle passing through the two poles of the celestial sphere and the zenith of a given observer.
- Mathematics A curve on a surface of revolution, formed by the intersection of the surface with a plane containing the axis of revolution.
- Mathematics 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.
- Archaic The highest point in the sky reached by the sun or another celestial body; a zenith.
- Archaic Noon.
- The highest point or stage of development; peak: "Men come to their meridian at various periods of their lives” ( John Henry Newman).
- Midwestern U.S. See median strip. See Regional Note at neutral ground.
- Of or relating to a meridian; meridional.
- Of or at midday: the meridian hour.
- Of, relating to, or constituting the highest point, as of development or power: the empire in its meridian period.