Definition of radius

The word "radius" has a fascinating history. It originates from Latin, where "radius" means "spoke" or "beam of light". In ancient Roman engineering, a radius referred to a Beam of light or a ray of light that shot from the center of a circle to its circumference. This term was later applied to the geometric concept of a line from the center of a circle to its edge, which is now known as the radius. In the 16th century, the Swiss mathematician and astronomer Johannes Kepler used the Latin term "radius" to describe the line from the center of a circle to its circumference, unknowingly changing the meaning of the word. The term "radius" was later adopted into the English language and is now widely used in mathematics, physics, and other fields to describe the distance from the center of a circle or sphere to its edge.