/ray"dee euhs/ , n. , pl. radii /-dee uy'/ , radiuses .
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.
[ 1590-1600; 1 ]