A crunode, also known as an ordinary double point, of a plane curve is point where a curve intersects itself so that two branches of the curve have distinct tangent lines. The Maclaurin trisectrix, shown above, has a crunode at the origin.

CITE THIS AS:

Weisstein, Eric W. "Crunode." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/Crunode.html