1. the radius of the circle of curvature; the absolute value of the reciprocal of the curvature of a curve at a given point;

The Collaborative International Dictionary of English v.0.48:

Radius \Ra"di*us\ (r[=a]"d[i^]*[u^]s), n.; pl. L. Radii (r[=a]"d[i^]*[imac]); E. Radiuses (r[=a]"d[i^]*[u^]s*[e^]z). [L., a staff, rod, spoke of a wheel, radius, ray. See Ray a divergent line.] 1. (Geom.) A right line drawn or extending from the center of a circle to the periphery; the semidiameter of a circle or sphere. [1913 Webster] 2. (Anat.) The preaxial bone of the forearm, or brachium, corresponding to the tibia of the hind limb. See Illust. of Artiodactyla. [1913 Webster] 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. [1913 Webster] 3. (Bot.) A ray, or outer floret, of the capitulum of such plants as the sunflower and the daisy. See Ray, 2. [1913 Webster] 4. pl. (Zool.) (a) The barbs of a perfect feather. (b) Radiating organs, or color-markings, of the radiates. [1913 Webster] 5. The movable limb of a sextant or other angular instrument. --Knight. [1913 Webster] Radius bar (Mach.), a bar pivoted at one end, about which it swings, and having its other end attached to a piece which it causes to move in a circular arc. Radius of curvature. See under Curvature. [1913 Webster]The Collaborative International Dictionary of English v.0.48:

Curvature \Cur"va*ture\ (k?r"v?-t?r; 135), n. [L. curvatura. See Curvate.] 1. The act of curving, or the state of being bent or curved; a curving or bending, normal or abnormal, as of a line or surface from a rectilinear direction; a bend; a curve. --Cowper. [1913 Webster] The elegant curvature of their fronds. --Darwin. [1913 Webster] 2. (Math.) The amount of degree of bending of a mathematical curve, or the tendency at any point to depart from a tangent drawn to the curve at that point. [1913 Webster] Aberrancy of curvature (Geom.), the deviation of a curve from a circular form. Absolute curvature. See under Absolute. Angle of curvature (Geom.), one that expresses the amount of curvature of a curve. Chord of curvature. See under Chord. Circle of curvature. See Osculating circle of a curve, under Circle. Curvature of the spine (Med.), an abnormal curving of the spine, especially in a lateral direction. Radius of curvature, the radius of the circle of curvature, or osculatory circle, at any point of a curve. [1913 Webster]WordNet (r) 3.0 (2006):

radius of curvature n 1: the radius of the circle of curvature; the absolute value of the reciprocal of the curvature of a curve at a given point