conchoid

Etymology
From (from )  or directly from, referring to the curved outline of a mussel shell or anything in this form.

Noun

 * 1)  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).
 * The conchoid of a circle with respect to a point on the circle is a cardioid if the fixed distance is equal to the diameter of the circle.
 * The Conchoid of Nicomedes is the conchoid of a straight line with respect to a point not on the line.
 * 1) * 1815, Charles Hutton, Pappus, entry in A Philosophical and Mathematical Dictionary, Volume 2, page 147,
 * He next treats of the properties of the Conchoid, which Nicomedes invented for doubling the cube; applying it to the solution of certain problems concerning Inclinations, with the finding of two mean proportionals, and cubes in any proportion whatever.
 * 1)  A conchoidal fracture in rock.
 * 1)  A conchoidal fracture in rock.
 * 1)  A conchoidal fracture in rock.
 * 1)  A conchoidal fracture in rock.

Usage notes
The fixed point (P) of the construction may be referred to as the of the conchoid; it may also be defined as the origin (of a Cartesian coordinate system) or the pole (if polar coordinates are used), and potentially referred to accordingly. The curve C is an example of a directrix.

Translations

 * Czech: konchoida
 * Russian:
 * Turkish: konkoid