1. one of the imaginary lines that goes around the Earth from the North Pole to the South Pole. These are used for measuring position, time etc.
2. an imaginary line that connects points of energy in your body, used by doctors who treat people using acupuncture
Origin of the word
A word first used in English during the late 14th century, meridian originates from the French ‘meridien’ meaning ‘of the noon time’, and the Latin ‘meridianum’, a literal translation of which is ‘middle day’.
In geography, meridian refers to a line of longitude on the Earth, making up one half of an imagined circle. The line passes through a position on the surface of the Earth, then connects with both the North and South Poles. To mark a specific point on the meridian between north and south, a latitude measurement is also required.
In astronomy, the word is often used because at noon the sun crosses the meridian, although this rarely corresponds to measured clock time on Earth. In acupuncture and for practitioners of Chinese medicine, the meridian is a collection of conduits in the human body through which energy is believed to flow.
Working from the Royal Observatory in Greenwich, London, the astronomer Edmond Halley first took meridian measurements in 1721. These brought about the idea of a point zero or a Prime Meridian, which would pass through Greenwich. Using this line of longitude as orientation, countries around the world began to keep their own local time.
“The astronomer is, in some measure, independent of his fellow astronomer; he can wait in his observatory till the star he wishes to observe comes to his meridian; but the meteorologist has his observations bounded by a very limited horizon, and can do little without the aid of numerous observers furnishing him contemporaneous observations over a wide-extended area.”
(James Pollard Espy)