radius

Concise Oxford English Dictionary © 2008 Oxford University Press:
radius /ˈreɪdɪəs/

▶noun (pl. radii /-dɪʌɪ/ or radiuses)

• 1 a straight line from the centre to the circumference of a circle or sphere.

  ■ a radial line from the focus to any point of a curve.

• 2 a specified distance from a centre in all directions: there are plenty of pubs within a two-mile radius.

• 3 Anatomy & Zoology a bone of the forearm or forelimb, in humans the thicker and shorter of two.

• 4 Zoology a radially symmetric feature in an echinoderm or coelenterate, e.g. an arm of a starfish.

• 5 Entomology a main vein in an insect's wing.

▶verb (radiuses, radiusing, radiused) (often as adj. radiused) make (a corner or edge) rounded.

– origin C16: from L., lit. ‘staff, spoke, ray’.