limaçon

Century Dictionary and Cyclopedia

1. n. Any univalve shell.
2. n. A curve, invented and named by Pascal, generated from a circle by adding a constant length to all the radii vectores drawn from a point of its circumference as an origin, taking proper account of negative radii vectores. It is a Cartesian, having cusps on the circular points; and it has a single bitangent, which is always real. It has three varieties, all of which are unicursal curves of the fourth order. One of these is the cardioid, which is a single form lying between the other two. It is of the third class. It has no node, but a cusp at the origin, and has no inflections. (See cut under cardioid.) All other limaçons are of the fourth class. Those lying outside of the cardioid have the origin as an acnode, and two real inflections; those lying within the cardioid have a crunode at the origin, and two imaginary inflections. For a crunodal limaçon, see Cartesian, n., 2.

Wiktionary

1. n. geometry A plane curve with polar equation or , of which the cardioid is a special case.

GNU Webster's 1913

1. n. (Geom.) A curve of the fourth degree, invented by Pascal. Its polar equation is r = a cos θ + b.