Pronunciation: (rā'dē-us),[key] —n., —pl.-di•iPronunciation: (-dē-ī"),[key]-di•us•es. 1. a straight line extending from the center of a circle or sphere to the circumference or surface: The radius of a circle is half the diameter. 2. the length of such a line.
3. any radial or radiating part.
4. a circular area having an extent determined by the length of the radius from a given or specified central point: every house within a radius of 50 miles. 5. a field or range of operation or influence.
6. extent of possible operation, travel, etc., as under a single supply of fuel: the flying radius of an airplane. 7. Anat.the bone of the forearm on the thumb side. Cf. ulna (def. 1). See diag. under skeleton. 8. Zool.a corresponding bone in the forelimb of other vertebrates.
9. Mach. Now Rare.the throw of an eccentric wheel or cam.
10. a rounded corner or edge on a machined or cast piece of metal.
11. Entomol.one of the principal longitudinal veins in the anterior portion of the wing of an insect.