cusp

cusp

1. A point or pointed end.
2. Anatomy
   a. A pointed or rounded projection on the chewing surface of a tooth.
   b. A triangular fold or flap of a heart valve.
3. Mathematics A point at which a curve crosses itself and at which the two tangents to the curve coincide.
4. Architecture The point of intersection of two ornamental arcs or curves, such as the inner points of a trefoil.
5. Astronomy Either point of a crescent moon.
6. A transitional point or time, as between two astrological signs.

Origin: Latin cuspis, point.