CONCHOID

Etymology

Noun

conchoid (plural conchoids)

(mathematics, geometry) 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).

(geology) A conchoidal fracture in rock.

Usage notes

The fixed point (P) of the construction may be referred to as the focus 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.

Source: Wiktionary

Con"choid, n. Etym: [Gr. conchoïde.] (Geom.)

Definition: A curve, of the fourth degree, first made use of by the Greek geometer, Nicomedes, who invented it for the purpose of trisecting an angle and duplicating the cube.

Source: Webster’s Unabridged Dictionary 1913 Edition