[ mə'rɪdɪən ]
■ noun
1》 a circle of constant longitude passing through a given place on the earth's surface and the poles.
↘ Astronomy a circle passing through the celestial poles and the zenith of a given place on the earth's surface.
2》 (in acupuncture and Chinese medicine) a pathway in the body along which vital energy is said to flow.
Origin
ME: from OFr. meridien , from L. ~um 'noon', from medius 'middle' + dies 'day'; the astronomy use is due to the fact that the sun crosses a ~ at noon.