strophoid

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The curve traced out by points P and Pˌ which lie on lines through a fixed point A where the midpoint M of PPˌ is on a fixed line and the absolute value }PM} = the absolute value }PˌM} = the absolute value }MO}, where O is the projection of A onto that fixed line.

Century Dictionary and Cyclopedia

1. n. A nodal plane cubic curve which is the locus of a focus of a conic whose directrix and two tangents are given.
2. n. A curve which is the locus of intersections of two lines rotating uniformly with commensurable velocities. See also suhstrophoid.