1.(Geom.) A right line drawn or extending from the center of a circle to the periphery; the semidiameter of a circle or sphere.
2.(Anat.) The preaxial bone of the forearm, or brachium, corresponding to the tibia of the hind limb. Note: The radius is on the same side of the limb as the thumb, or pollex, and in man it is so articulated that its lower end is capable of partial rotation about the ulna.
5.The movable limb of a sextant or other angular instrument.