radius

n. (pl. Radii or radiuses) 1 a straight line from the centre to the circumference of a circle or sphere. B length of this. 2 distance from a centre (within a radius of 20 miles). 3 a thicker and shorter of the two bones in the human forearm. B corresponding bone in a vertebrate's foreleg or a bird's wing. [latin]

n. A right line drawn or extending from the center of a circle to the periphery; the semidiameter of a circle or sphere.