Definitions of radius:

noun: the length of a line segment between the center and circumference of a circle or sphere
noun: the outer and slightly shorter of the two bones of the human forearm
noun: a circular region whose area is indicated by the length of its radius
Example: "They located it within a radius of 2 miles"
noun: a straight line from the center to the perimeter of a circle (or from the center to the surface of a sphere)
noun: support consisting of a radial member of a wheel joining the hub to the rim