radius

Abbr. r or rad. Mathematics

1. A line segment that joins the center of a circle with any point on its circumference.

2. A line segment that joins the center of a sphere with any point on its surface.

3. A line segment that joins the center of a regular polygon with any of its vertices.

4. The length of any such line segment.

5. A long, prismatic, slightly curved bone, the shorter and thicker of the two forearm bones, located on the lateral side of the ulna.

6. A similar bone in many vertebrates.

A circular area measured by a given radius: every family within a radius of 25 miles of the city center.

A bounded range of effective activity or influence: the operating radius of a helicopter.

A radial part or structure, such as a mechanically pivoted arm or the spoke of a wheel.

Anatomy

1. A long, prismatic, slightly curved bone, the shorter and thicker of the two forearm bones, located on the lateral side of the ulna.

2. A similar bone in many vertebrates.