Definition of: cissoid

(sis′oid) Math. noun
A curve GAP intersecting a circle at the two extremities of a diameter and having a cusp the apex of which is at the point on the circumference where the perpendicular bisector of the diameter falls: the curve traces the locus of a point moving so that a straight line BC drawn through the apex of the cusp at A through the curve at any point Ρ intersects the tangent DEF (with E on the circumference diametrically opposite to A) at point M, so that AP = NM.
—adjective Contained within two curves that intersect each other, as an angle: opposed to sistroid: The angle interior to both curves is a cissoid angle; the exterior and opposite a sistroid. [<Gk. kissoeidēs like ivy <kissos ivy + eidos form]
CISSOID