radius

n. & v.
—n. (pl. radii or radiuses)
1 Math. a a straight line from the centre to the circumference of a circle or sphere. b a radial line from the focus to any point of a curve. c the length of the radius of a circle etc.
2 a usu. specified distance from a centre in all directions (within a radius of 20 miles; has a large radius of action).
3 a the thicker and shorter of the two bones in the human forearm (cf. ULNA). b the corresponding bone in a vertebrate's foreleg or a bird's wing.
4 any of the five arm-like structures of a starfish.
5 a any of a set of lines diverging from a point like the radii of a circle. b an object of this kind, e.g. a spoke.
6 a the outer rim of a composite flower-head, e.g. a daisy. b a radiating branch of an umbel.
—v.tr. give a rounded form to (an edge etc.).
Phrases and idioms:
radius vector Math. a variable line drawn from a fixed point to an orbit or other curve, or to any point as an indication of the latter's position.
Etymology: L, = staff, spoke, ray