noun
octant
A navigational instrument used for measuring angles, especially in celestial navigation. The term is technical and primarily encountered in historical or maritime contexts.
八分儀は、18世紀の航海で広く使われた。
The octant was widely used in 18th-century navigation.
From 八分 (one-eighth) + 儀 (instrument). The name reflects the instrument's 45-degree arc, which is one-eighth of a circle.