Radius /(rā"dĭ*ŭs)/

Ra·di·us

Radius

n.

pl. Radii, Radiuses ((rā"dĭ*ī))

  1. A right line drawn or extending from the center of a circle to the periphery; the semidiameter of a circle or sphere. (Geom.)
  2. The preaxial bone of the forearm, or brachium, corresponding to the tibia of the hind limb. See Illust. of Artiodactyla. (Anat.)
  3. A ray, or outer floret, of the capitulum of such plants as the sunflower and the daisy. See Ray, 2. (Bot.)
  4. The barbs of a perfect feather. (Zool.)
  5. The movable limb of a sextant or other angular instrument.

Phrases & Compounds
Radius bar
a bar pivoted at one end, about which it swings, and having its other end attached to a piece which it causes to move in a circular arc.
Radius of curvature
See under Curvature.