radius

Radius is a line from the center to the outside of a circle or sphere.

(noun)

An example of radius is the spoke a bike wheel.

The definition of a radius is a circular limit or a boundary of a specific distance which is drawn from a specific point.

(noun)

An example of radius is a restaurant located within five miles of a house.

See radius in Webster's New World College Dictionary

noun pl. radii or radiuses

a raylike or radial part, as a spoke of a wheel
1. any straight line extending from the center to the periphery of a circle or sphere
2. the length of such a line
1. the circular area or distance limited by the sweep of such a line: no house within a radius of five miles
2. the distance a ship or airplane can travel and still return to its point of origin without refueling
an extent, scope, range, etc. of a limited or specified kind: within the radius of one's experience
1. the shorter and thicker of the two bones of the forearm on the same side as the thumb
2. a corresponding bone of the forelimb of a four-legged animal
Zool.
1. any of the planes of division of the body of a radially symmetrical animal
2. any of various longitudinal veins in the wing of an insect

Origin: L, rod, spoke (of a wheel), hence radius, ray (of light), ? akin to radix, root

See radius in American Heritage Dictionary 4

noun pl. ra·di·i (-dē-īˌ) or ra·di·us·es

Abbr. r or rad. Mathematics
a. A line segment that joins the center of a circle with any point on its circumference.
b. A line segment that joins the center of a sphere with any point on its surface.
c. A line segment that joins the center of a regular polygon with any of its vertices.
d. 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. A long, prismatic, slightly curved bone, the shorter and thicker of the two forearm bones, located on the lateral side of the ulna.
b. A similar bone in many vertebrates.