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):

curvature
    n 1: (medicine) a curving or bending; often abnormal; "curvature
         of the spine"
    2: the rate of change (at a point) of the angle between a curve
       and a tangent to the curve
    3: the property possessed by the curving of a line or surface
       [syn: curvature, curve]