Medical Definition of radius
plural ra·dii \-ē-ˌī\play also ra·di·us·es
: the bone on the thumb side of the human forearm or on the corresponding part of the forelimb of vertebrates above fishes that in humans is movably articulated with the ulna at both ends so as to permit partial rotation about that bone, that bears on its inner aspect somewhat distal to the head a prominence for the insertion of the biceps tendon, and that has the lower end broadened for articulation with the proximal bones of the carpus so that rotation of the radius involves also that of the hand
Seen and Heard
What made you want to look up radius? Please tell us where you read or heard it (including the quote, if possible).