antipoint

Century Dictionary and Cyclopedia

1. n. One of a pair of foci, real or imaginary, to a plane curve, so related to another pair that if a quadrilateral be drawn having the two foci of each pair at opposite angles, the opposite sides will meet at the circular points at infinity, and consequently be tangent to the curve.
2. n. Given any system of coaxal circles, another system of coaxal circles may be constructed such that every circle of either system cuts orthogonally every circle of the other system. The limiting points of either system are the antipoints of the limiting points of the other system.