n., pl., -di·i (-dē-ī'), or -di·us·es.
- (Abbr. r or rad.) Mathematics.
- A line segment that joins the center of a circle with any point on its circumference.
- A line segment that joins the center of a sphere with any point on its surface.
- A line segment that joins the center of a regular polygon with any of its vertices.
- 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.
- A similar bone in many vertebrates.
[Latin, ray, spoke of a wheel, radius.]
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
