Math. In 7 cissoeide. [ad. Gr. κισσοειδ-ής ivy-like, f. κισσό-ς ivy: see -OID. The cusp of the cissoid resembles the re-entrant angles of an ivy-leaf.]
1. A curve of the second order invented by Diocles.
If from any two points lying on a fixed diameter of a circle, and equidistant from the center, perpendiculars be drawn to the circumference, and a straight line be drawn from one extremity of the diameter to that of either perpendicular, the locus of the point in which this straight line cuts the other perpendicular will be a cissoid of Diocles, having its cusp at the end of the diameter. In later times the term has been extended to curves similarly described, where the generating curve is not a circle.
1656. trans. Hobbes’ Elem. Philos., 12.
1694. Halley, Method finding Roots of Equations, in Misc. Cur. (1708), II. 70. By the help of the Parabola, Cissoid, or any other Curve.
1798. Loves of Triangles, I. 11, in Anti-Jacobin, 16 April. For me, ye Cissoids, round my temples bend Your wandering curves.
1879. Salmon, Higher Plane Curves, V. 182. If a parabola roll on an equal one, the locus of the vertex of the moving parabola will be the cissoid.
2. Cissoid angle.
1751. Chambers, Cycl., s.v. Angle, Cissoid Angle … is the inner angle made by two spherical convex lines intersecting each other.
So 1796. Hutton, Dict. Math., s.v. Angle.
Hence Cissoidal a., pertaining to a cissoid.
1796. Hutton, Math. Dict., s.v. Cissoid, The whole infinitely long cissoidal space, contained between the infinite asymptote … and the curves … of the cissoid, is equal to triple the generating circle.
