Cusp

Etymology
From cuspis:; first used in astrology.

Noun

 * 1) A sharp point or pointed end.
 * 2)  An important moment when a decision is made that will determine future events.
 * 3)  A point of a curve where the curve is continuous but has no derivative, but such that it has a derivative at every nearby point.
 * 4)  A boundary between zodiacal signs and houses.
 * 5)  Any of the pointed parts of a canine tooth or molar.

Derived terms

 * cusp form
 * cusp neighborhood, cusp neighbourhood
 * cusped

Related terms

 * bicuspid
 * cusper
 * cuspid
 * tricuspid