radius

 
Pronunciation: /ˈreɪdɪəs/

noun (plural radii /-dɪʌɪ/ or radiuses)

  • 1a 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.
  • a specified distance from a centre in all directions: there are plenty of local pubs within a two-mile radius
  • 2 Anatomy the thicker and shorter of the two bones in the human forearm. Compare with ulna.
  • Zoology the bone in a vertebrate’s foreleg or a bird’s wing that corresponds to the radius in a human being.
  • Entomology any of the main veins in an insect’s wing.
  • 3 Zoology a radially symmetric feature in an echinoderm or coelenterate, e.g. an arm of a starfish.

verb (radiuses, radiusing, radiused)

[with object] (often as adjective radiused)
  • give a rounded form to (a corner or edge).

Origin:

late 16th century (in radius (sense 2 of the noun)): from Latin, literally 'staff, spoke, ray'

Spelling help

The plural of radius can be spelled either radii (as in the original Latin) or radiuses.