RADIUS

noun (plural radii; also ~es) Etymology: Latin, ray, ~ Date: circa 1611 a line segment extending from the center of a circle or sphere to the circumference or bounding surface, 2. the bone on the thumb side of the human forearm, the third and usually largest vein of an insect's wing, 3. the length of a ~ , the circular area defined by a stated ~, a bounded or circumscribed area, a radial part, the distance from a center line or point to an axis of rotation