trigon

noun6

1. •
   (rare) A triangle.
2. •
   The cusp (cutting region) of the crown of an upper molar, usually the anterior part.
3. •
   A division consisting of three star signs.

   • The Cancer trigon is composed of Cancer, Scorpio and Pisces
4. •
   (historical) An ancient triangular harp of Oriental origin which had four strings and was often used for banquet music. Also called sabbeka, sackbut, sambuca.
5. •
   A trine; an aspect of two planets distant 120 degrees from each other.

   • In the horoscope of Christ's nativity.[…]Whether a trigon or no, this tetragon I am sure there was. — 1626
6. •
   (historical) An old ball game played by three people standing in a triangular formation. (See Wikipedia's entry for the game)