Let the center of a Circle of Radius move along a line . Let be a fixed point located a distance away from . Draw a Secant Line through and , the Midpoint of the chord cut from the line (which is parallel to ) and a distance away. Then the Locus of the points of intersection of and the Circle and is called a kieroid.
Yates, R. C. ``Kieroid.'' A Handbook on Curves and Their Properties. Ann Arbor, MI: J. W. Edwards, pp. 141-142, 1952.