cusp

American Heritage® Dictionary of the English Language, Fourth Edition

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

Century Dictionary and Cyclopedia

1. n. In astronomy, the point or horn of a crescent, specifically of the crescent moon.
2. n. In astrology, the beginning or first entrance of any house in the calculation of nativities.
3. n. In geometry, a stationary point on a curve, where a point describing the curve has its motion precisely reversed.
4. n. In architecture, an intersecting point of the small arcs or foliations decorating the internal curves of the trefoils, cinquefoils, etc., of medieval tracery; also, the figure formed by the intersection of such arcs.
5. n. In zoöl. and anatomy:
6. n. Any special prominence or protuberance of the crown of a tooth. A blunt conical cusp is called a tubercle; a sharp sectorial cusp is a blade; a low or lateral cusp is a heel. Teeth are sometimes named from the number of their cusps, as bicuspid, tricuspid. A canine tooth, the crown of which consists of a single cusp, is cuspidate.
7. n. A sharp tooth-like process on a margin or part.
8. n. In botany, a sharp and rigid point, as of a leaf.
9. n. One of the segments, with pointed tip, of a valve of the heart.

Wiktionary

1. n. A sharp point or pointed end.
2. n. figuratively An important moment when a decision is made that will determine future events.
3. n. geometry 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. n. astrology A boundary between zodiacal signs and houses.
5. n. dentistry Any of the pointed parts of a canine tooth or molar.

GNU Webster's 1913

1. n. (Arch.) A triangular protection from the intrados of an arch, or from an inner curve of tracery.
2. n. (Astrol.) The beginning or first entrance of any house in the calculations of nativities, etc.
3. n. (Astron) The point or horn of the crescent moon or other crescent-shaped luminary.
4. n. (Math.) A multiple point of a curve at which two or more branches of the curve have a common tangent.
5. n. (Anat.) A prominence or point, especially on the crown of a tooth.
6. n. (Bot.) A sharp and rigid point.
7. v. To furnish with a cusp or cusps.

WordNet 3.0

1. n. a thin triangular flap of a heart valve
2. n. small elevation on the grinding surface of a tooth
3. n. point formed by two intersecting arcs (as from the intrados of a Gothic arch)