lune

Lune is a term with several meanings in language and science. In French, lune means the Moon, Earth’s natural satellite, and the word appears in astronomy, literature, and everyday speech. In English, lune also denotes a geometric shape: a crescent formed by the difference between two circular discs or arcs.

Etymology and usage: The word derives from Latin luna, via Old French lune, reflecting its original association with the Moon. The geometric sense is named for its crescent-like appearance and is used in discussions of plane geometry and area.

Geometry: A lune is a plane figure bounded by circular arcs. It is the region between two arcs that intersect, producing a crescent-like shape. The study of lunes has a historical note of importance: Hippocrates of Chios showed that some lunes could have areas equal to a triangle, illustrating a surprising connection between curved and straight figures and contributing to early geometric theory.

Geography: The River Lune is a river in north-west England, flowing through Cumbria and Lancashire and passing the city of Lancaster. Its valley is known as the Lune Valley, a feature of the region’s landscape and history.

Other uses: Lune can appear as a surname or in place names in various languages, but its primary contemporary references are the Moon in French, the geometric lune in mathematics, and the English river Lune. The term is rarely used as a standalone English noun outside these contexts.