Geom. [Irreg. f. L. spīna spine + NODE sb.] A stationary point on a curve; a cusp.
1852. Cayley, Math. Papers (1889), II. 28. I shall, with reference to plane curves,… use the term ‘node’ as synonymous with double point, and the term ‘spinode’ as synonymous with cusp.
1852. G. Salmon, Higher Plane Curves, ii. (1879), 25. Such points are called cusps or spinodes. They are also called stationary points.
attrib. 1852. Cayley, Math. Papers (1889), II. 29. The spinode-planes give rise to a developable which may be termed the ‘spinode-develope.’ Also the ‘spinode-tangent’ is the tangent to the curve of intersection at the spinode. Ibid. (1869), (1893), VI. 450. The spinode curve of the cubic surface. Ibid., 584. The spinode torse is the envelope of the parabolic planes of the surface.
