Definition:Circle/Radius

Definition

 * Circle.png

A radius of a circle is a straight line segment whose endpoints are the center and the circumference of the circle.

In the above diagram, the line $AB$ is a radius.

Linguistic Note
The plural of radius is radii, pronounced ray-dee-eye.

This irregular plural form stems from the Latin origin of the word radius, meaning ray

The ugly incorrect form radiuses can apparently be found, but rarely in a mathematical context.