cusp

cusp is a   Noun

Definition:

[1] A triangular protection from the intrados of an arch, or from an inner curve of tracery.

[2] The beginning or first entrance of any house in the calculations of nativities, etc.

[3] The point or horn of the crescent moon or other crescent-shaped luminary.

[4] A multiple point of a curve at which two or more branches of the curve have a common tangent.

[5] A prominence or point, especially on the crown of a tooth.

[6] A sharp and rigid point.

Synonyms: