centre of curvature

noun
  1. the point on the normal at a given point on a curve on the concave side of the curve whose distance from the point on the curve is equal to the radius of curvature
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012