trigon

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A triangular lyre or harp of Roman and Greek antiquity.
• noun Archaic A triangle.

from The Century Dictionary.

• noun The prominent anterior portion of an upper molar tooth forming a triangular area at whose angles are the three principal cusps —the protocone, paracone, and metacone. The study of the Mesozoic mammals has left no doubt that the upper and lower triangles, or ‘trigon’ and ‘trigonid,’ were derived from the reptilian protocone by the addition of lateral cusps. See cut under tooth, 1.
• noun An abbreviation of trigonometrical; of trigonometry.
• noun A trig; a skid.
• noun A triangle.
• noun In astrology: The junction of three signs, the zodiac being divided into four trigons: the watery trigon, which includes Cancer, Scorpio, and Pisces; the earthly trigon, Taurus, Virgo, and Capricornus; the airy trigon, Gemini, Libra, and Aquarius; and the fiery trigon, Aries, Leo, and Sagittarius.
• noun Trine: an aspect of two planets distant 120 degrees from each other.
• noun In antiquity: A kind of triangular lyre or harp. Also called trigonon.
• noun A game at ball played by three persons standing so as to be at the angles of a triangle.
• noun An instrument of a triangular form, used in dialing.
• noun In conchology, a shell of the genus Trigonia.

from the GNU version of the Collaborative International Dictionary of English.

• noun A figure having three angles; a triangle.
• noun A division consisting of three signs.
• noun Trine, an aspect of two planets distant 120 degrees from each other.
• noun A kind of triangular lyre or harp.
• noun A kind of game at ball played by three persons standing at the angular points of a triangle.
• noun (Zoöl.) The cutting region of the crown of an upper molar, usually the anterior part. That of a lower molar is the Tri"go*nid (�).

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun geometry, rare A triangle.
• noun An ancient triangular harp of Oriental origin which had four strings and was often used for banquet music. Also called sabbeka, sackbut, sambuca.
• noun astrology A division consisting of three signs.
• noun astrology A trine; an aspect of two planets distant 120 degrees from each other.
• noun An old ball game played by three people standing in a triangular formation.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a three-sided polygon
• noun (astrology) one of four groups of the zodiac where each group consists of three signs separated from each other by 120 degrees
• noun a triangular lyre of ancient Greece and Rome