(pl radii /rā'di-ī/ or ra'diuses) a straight line from the centre to the circumference of a circle or surface of a sphere (geom); a radiating line; anything placed like a radius, such as the spoke of a wheel, the movable arm of a sextant, etc; a radial plane of symmetry in a coelenterate; a line from a fixed point (eg the focus of a conic) to a point on a curve; the outer bone (in supine position) of the forearm in humans, or its equivalent in other animals; a barbule of a feather; the third vein of an insect's wing; a ray-flower or the ray-flowers of a head collectively (rare); a distance from a centre, conceived as limiting an area or range. [L radius a rod, spoke, ray]
n pl -dii (-dɪˌaɪ) or -diuses 1 a straight line joining the centre of a circle or sphere to any point on the circumference or surface 2 the length
1. (plural radii /'reIdiaI/ /'raydeeuy/ radiuses) a straight line extending from the centre of a circle or sphere to the circumference or surface.
1 (Math.) The line segment joining the centre of a circle to any point on it, or the length of such a line. 2 (Biol.) One of the two bones of