
Mathematics A line segment that joins the center of a circle with any point on its circumference.
(noun)

Mathematics A line segment that joins the center of a sphere with any point on its surface.
(noun)

Mathematics A line segment that joins the center of a regular polygon with any of its vertices.
(noun)

Mathematics The length of any such line segment.
(noun)

A circular area measured by a given radius: every family within a radius of 25 miles of the city center.
(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.