binoden.
/ˈbʌɪnəʊd/ Geometry.
A point on a surface at which there are two tangent planes.
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the world > relative properties > number > geometry > point > [noun] > on a surface or plane
conical point1812
umbilicus1841
stigma1863
binode1869
branch-point1878
saddle point1907
saddle1952
1869 Cayley in Philos. Trans. (Royal Soc.) 159 201 Conical and biplanar nodes, or, as I call them, cnicnodes, and binodes.
1874 G. Salmon Treat. Analytic Geom. Three Dimensions (ed. 3) 457 The quadric cone may degenerate into a pair of planes. Such a node may be called a binode.
1934 D. M. Y. Sommerville Analyt. Geom. Three Dimensions xvii. 375 If the double-point at D is a binode, ax2 + … = 0 breaks up into two planes and the discriminant ∆ of this quadratic vanishes.
This entry has not yet been fully updated (first published 1933; most recently modified version published online June 2018).
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n.1869