radius

The distance from the center of a circle or ball to its outer edge.

• The radius is five centimeters.
• Double the radius to find the diameter.
• Several villages lie within a ten-kilometer radius of the school.

How to use it: a radius of something (The circle has a radius of four centimeters.); within a radius of something (Deliveries are free within a radius of five kilometers.)

Common phrases: radius of something, within a radius, five kilometer radius

A straight line from the center of a circle or ball to its outer edge.

• Draw a radius from the center.
• Each radius meets the circle at its edge.
• The diagram shows two radii forming an angle.

How to use it: the radius of something (Draw a radius of the circle in red.)

Common phrases: draw a radius, radius of something, circle radius

One of the two main bones in the lower part of an arm or animal foreleg.

• She broke her radius.
• The surgeon examined the lower end of the radius.
• The animal has a short radius beside its ulna.

Common phrases: radius and ulna, fractured radius, distal radius