Definition of radius in English:

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Pronunciation: /ˈreɪdɪəs/

noun (plural radii /ˈreɪdɪʌɪ/ or radiuses)

Image of radius
1A straight line from the centre to the circumference of a circle or sphere.
Example sentences
  • Thus, the area of a circle is equal to half of the product of the radius and the circumference.
  • He calculates the side of a regular pentagon in terms of the radius of the circumscribed circle.
  • Recall that given a circle of radius r, the circumference is 2pr.
1.1A radial line from the focus to any point of a curve.
Example sentences
  • These apply to clear zones on the outside of horizontal curves with a radius of 900 m or less.
  • Key factors to meet the new criteria include the length and width of runways, the width and curve radii of taxiways, and also the airport's pavement loading limits.
  • Second, this lightweight insert extends the bullet nose and accommodates use of a longer ogive - the radius of the curve of the bullet tip.
1.2A specified distance from a centre in all directions: there are plenty of local pubs within a two-mile radius
More example sentences
  • It seems sensible to find somewhere with no population centres within a two-mile radius - like offshore.
  • The department has acquired legal powers to close all footpaths within a two-mile radius of any free-range poultry farms.
  • Teams divided into four groups, combing through a two-mile radius searching for any clue of what might have happened.
2 Anatomy The thicker and shorter of the two bones in the human forearm. Compare with ulna.
Example sentences
  • Common osteoporotic fracture sites include the vertebrae, the hip, the distal radius of the forearm, and the proximal humerus.
  • Scaphoid fractures are rare children and the elderly because of the relative weakness of the distal radius compared with the scaphoid in these age groups.
  • Abduction is movement of the hand away from the body as the proximal carpal bones move medially on the radius.
2.1 Zoology The bone in a vertebrate’s foreleg or a bird’s wing that corresponds to the radius in a human being.
Example sentences
  • For example, the radius, one of the lower bones of the foreleg, became much broader.
  • As is usual in chelonioids, the radius is notably longer than the ulna.
  • In the equid foreleg, radius and ulna are united, and the ulna is greatly reduced so that all weight is born on the radius.
2.2 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).
Example sentences
  • The carry bevel package is subtle, radiused by hand using emery sticks, with the sharp edges are gently broken, not belt-sanded into oblivion.
  • All of the outer edges of the handle are radiused, making for a comfortable grip.
  • Brian carefully radiused all the sharp edges and corners, blending them gently by hand with file strokes.


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

For editors and proofreaders

Line breaks: ra¦dius

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