conchoid
noun Any of a family of curves defined as the locus of points ''p'', such that each ''p'' is on a line that passes through a given fixed point ''P'' and intersects a given curve, ''C'', and the distance from ''p'' to the point of intersection with ''C'' is a specified constant (note that for nontrivial cases two such points ''p'' satisfy the criteria, and the resultant curve has two parts)