Definition of radius in English:



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

    • ‘The radii of the given circles and n must stand in a certain relationship for the chain to close on itself.’
    • ‘Given an angle CAB draw a circle with centre A so that AC and AB are radii of the circle.’
    • ‘Recall that given a circle of radius r, the circumference is 2pr.’
    • ‘He calculates the side of a regular pentagon in terms of the radius of the circumscribed circle.’
    • ‘The particular tablet which interests us here investigates how to calculate the radius of a circle through the vertices of an isosceles triangle.’
    • ‘In the introduction he pointed out that a plane was a special case of a spherical surface, that is a sphere with infinite radius.’
    • ‘Note that this curvature is the inverse of the radius of a circle tangent to the neutral line at this point.’
    • ‘David Gregory used p/r for the ratio of the circumference of a circle to its radius.’
    • ‘So the radius of the sphere will be 1 and its surface area will be 4 Pi.’
    • ‘Because the slices are thin, the height of the rectangle is approximately the radius, r, of the circle.’
    • ‘Users can measure the distance of vertices/edges/faces, the angle of edges/faces, and the radii and diameters of circles.’
    • ‘A circle and square have an equal area only if the ratio between a side of the square and a radius of the circle equals the square root of pi.’
    • ‘Company officials like to say that Rhino can go beyond high-school geometry, beyond straight lines and radiuses.’
    • ‘Thus, the area of a circle is equal to half of the product of the radius and the circumference.’
    • ‘The inverse of the radius of the circle equals the curvature in radians/m.’
    • ‘The point P is on the circumference of the circle of radius b.’
    • ‘And, if anything, I'm quite nearly positive that Lancome is the guy who discovered the constant ratio of a circle's radius to its circumference.’
    • ‘The hexagon is a function between the radius and circumference of the circle, and is a naturally occurring form in nature.’
    • ‘A circle of radius 6 is circumscribed by a square of side-length 12.’
    • ‘It states that the centre of gravity of a semicircle divides the radius in the ratio 3: 7.’
    1. 1.1 A radial line from the focus to any point of a curve.
      • ‘The upper three curves are the pore radii for the three systems, whereas the lower three are the corresponding standard deviations of the upper curves.’
      • ‘The front rolled edge and curved radius of this striking two-tiered kitchen island can only be accomplished in solid surface material such as granite or Corian (tm).’
      • ‘A minimum curve radius of 5 feet is suggested for 1/2-inch-diameter strand.’
      • ‘Because of the very mountainous terrain and the need for very shallow radius curves, most of the route will be in tunnels, with consequent heavy civil engineering costs.’
      • ‘Second, this lightweight insert extends the bullet nose and accommodates use of a longer ogive - the radius of the curve of the bullet tip.’
      • ‘The curve radii and crossfall of the road are measured and fed through algorithms from the Austroads Rural Road Design guide to generate a suggested advisory speed for all points along the road.’
      • ‘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.’
    2. 1.2 The length of the radius of a circle or sphere.
      • ‘Stephenson, who constructed both projects, believed that gradients should be less than 1 percent and that curves should have very wide radii of at least a kilometre.’
      • ‘The cone shaped tip is just under one micrometer in length and has a radius of a few nanometers at its apex.’
      • ‘As skaters pull their arms in, their radius decreases and they spin faster.’
      • ‘Interestingly, though the analysis points to a ball with an average radius of 1.584 inches, the measured radius of a real baseball is 1.452 inches.’
    3. 1.3 A specified distance from a centre in all directions.
      ‘there are plenty of local pubs within a two-mile radius’
      • ‘Tests results Tuesday showed that all 20 farms within a two mile radius of the original infected farm were negative for avian influenza.’
      • ‘It seems sensible to find somewhere with no population centres within a two-mile radius - like offshore.’
      • ‘I spent half a century here, most of it within the confines of a small radius.’
      • ‘We do not allow students who live within a five-mile radius to use their cars to come to college.’
      • ‘Once Keaton laughed so hard he scared all the birds within a ten-foot radius out of their perches.’
      • ‘The department has acquired legal powers to close all footpaths within a two-mile radius of any free-range poultry farms.’
      • ‘The explosions could reach a radius of 25 meters.’
      • ‘He concluded: ‘This year, I will enter half a dozen local races, all within a radius of 50 miles, and hope to do pretty well.’’
      • ‘Teams divided into four groups, combing through a two-mile radius searching for any clue of what might have happened.’
      • ‘Those deemed more at risk of exposure are those who lived within a one-kilometer radius of the factory for more than 20 years between 1962 and 1987.’
      • ‘Police are investigating links between the arson attack on December 27 and another three within a half-mile radius over the last few days.’
      • ‘But one recommendation to come out of it was that masts should not be located within a radius of 500 metres of schools and homes.’
      • ‘To calculate a radius for each hospital's market area, we limited radii to a range between 10 and 35 miles.’
      • ‘At half-mile intervals, they stop and count the birds they see or hear within a radius of a quarter mile.’
      • ‘The IT professionals usually look out for areas surrounding a radius of 9 km from City Railway Station.’
      • ‘Day said location is key when making an investment and believes investors should focus on the coastal strip within a 10-mile radius of the city.’
      • ‘B & Bs within a three-mile radius of the town were full.’
      • ‘The Ride Safe program provides rides for students, staff and faculty members from the Student Life Centre to their homes within a certain radius around campus.’
      • ‘A check of directories shows 37 hotels and motels within a three-mile radius of Florence and LaSalle.’
      • ‘It should be known in this connection that according to the relevant law, no structure of any kind can be built within a radius of 100 metres of any registered national monument.’
  • 2Anatomy
    The thicker and shorter of the two bones in the human forearm.

    Compare with ulna
    • ‘Abduction is movement of the hand away from the body as the proximal carpal bones move medially on the radius.’
    • ‘Bone mineral density was measured at the lumbar spine, radius, hip and femoral neck.’
    • ‘He also had tenderness bilaterally over the distal radius and ulna, and anterior tibia.’
    • ‘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.’
    1. 2.1Zoology The bone in a vertebrate's foreleg or a bird's wing that corresponds to the radius in a human being.
      • ‘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.’
      • ‘To fit a horse radius into a human forearm would require a physique to rival Popeye.’
      • ‘In the equid foreleg, radius and ulna are united, and the ulna is greatly reduced so that all weight is born on the radius.’
      • ‘The humerus, radius, and ulna of Adriosaurus appear to be slightly wider than those of the current specimen, but this is probably a result of crushing.’
    2. 2.2Entomology Any of the main veins in an insect's wing.
  • 3Zoology
    A radially symmetric feature in an echinoderm or coelenterate, e.g. an arm of a starfish.


[WITH OBJECT]often as adjective radiused
  • Give a rounded form to (a corner or edge).

    • ‘The ejector is a long Commander style, with the nose radiused.’
    • ‘The porte-cochere piers are composed of granite bases, banded brickwork with 1-inch radiused returns, and limestone caps.’
    • ‘Brian carefully radiused all the sharp edges and corners, blending them gently by hand with file strokes.’
    • ‘You can use a tube flange feature to put a radiused edge on an opening in a sheet-metal part and simultaneously extend it as a tube.’
    • ‘Their pleasantly radiused shape along with the secure pocket clip make this one of the most carry friendly folders I've ever used.’
    • ‘A radiused thumbhole is used to access the blade and, once again, a liner-lock secures it in place.’
    • ‘Its exactly the same width as the green perspex panel above it, with matching radiused corners.’
    • ‘The tool has a radiused ridge for cutting and edge sealing with the shape of the ridge similar to the shape desired for the edge seal.’
    • ‘After checkering the main spring housing at 25 lpi, it was fit and blended into the frame with the bottom corner radiused.’
    • ‘These flexible wings also blend successive passes and radius the outside edges of the skate lane to prevent ski tips from catching.’
    • ‘The sight was nicely radiused to match the trigger group and the two holes aligned just so.’
    • ‘The carry bevel package is subtle, radiused by hand using emery sticks, with the sharp edges are gently broken, not belt-sanded into oblivion.’
    • ‘A complete set would include a right and left pair, a ‘topping’ plane for the top, and radiused versions for curved sections.’
    • ‘In place of crisp corners, radiused edges - as in Tokyo Prada - create the illusion of a jointless architecture.’
    • ‘The lock's radiused, arc-shaped design permits maximum surface contact with the blade's tang.’
    • ‘All of the outer edges of the handle are radiused, making for a comfortable grip.’
    • ‘It is usual for the bar to have a suitable dimensional radiused groove, machined along its length to mould the penetration bead to a desired geometrical shape.’
    • ‘The only negative on this sixgun is that the backstrap is not radiused quite right where it bolts to the frame on both sides of the hammer.’
    • ‘The bottom rolls into the hull sides with a radiused turn rather than a sharp corner-like edge and there is long wine glass-shaped keel integral with the hull.’
    • ‘I used a 1/2-inch dry-grind diamond router bit to radius the top edges of the counter.’


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