Definition of "radius"

radius

/ˈɹeɪ.di.əs/

noun
plural radii or radiuses
1. (anatomy) The long bone in the forearm, on the side of the thumb.
  Quotations
  It is also obvious, and proved by experiment, that the rotatory motions observed in the hand proceed from the rotatory motions of the radius.
  1808, John Barclay, The Muscular Motions of the Human Body‎, page 396
2. (zoology) The lighter bone (or fused portion of bone) in the forelimb of an animal.
3. (entomology) One of the major veins of the insect wing, between the subcosta and the media; the vein running along the costal edge of the discal cell.
4. (geometry) A line segment between any point of a circle or sphere and its center.
5. (geometry) The length of this line segment.
6. Anything resembling a radius, such as the spoke of a wheel, the movable arm of a sextant, or one of the radiating lines of a spider's web.
  Quotations
  […] I can do more with a Quadrant, Sextant or Octant, of 1 foot Radius, furniſhed with Teleſcopical Sights and Screws, then [sic] can poſſibly be done with any other Inſtrument, furniſhed only with Common Sights, though 10, 20, 30, nay threeſcore foot Radius; […]
  1674, Robert Hooke, Animadversions on the Firſt Part of the Machina Coelestis of the […] Aſtronomer Johannes Hevelius […] ‎, page 43