a point on a curve or surface at which there can be more than one tangent line or tangent plane.
a point, line, or region in a standing wave at which there is relatively little or no vibration.
either of the two points at which the orbit of a heavenly body intersects a given plane, esp. the plane of the ecliptic or of the celestial equator. Cf.
an element of a tree diagram that represents a constituent of a linguistic construction.