A right line drawn or extending from the center of a circle to the periphery; the semidiameter of a circle or sphere.
- Mathematics A line segment that joins the center of a circle with any point on its circumference.
- Mathematics A line segment that joins the center of a sphere with any point on its surface.
- Mathematics A line segment that joins the center of a regular polygon with any of its vertices.
- Mathematics The length of any such line segment.
- 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 A long, prismatic, slightly curved bone, the shorter and thicker of the two forearm bones, located on the lateral side of the ulna.
- Anatomy A similar bone in many vertebrates.