radi/o is a combining form that refers to “radius (lateral forearm bone)”.
In the forearm, the radius is one of two bones, the other being the ulna. Its primary function is to connect to the ulna and humerus at the elbow to facilitate supination (rotation of the forearm that results in the palm of the hand facing up) and pronation (rotation of the forearm that results in the palm of the hand facing down).
