From The Collaborative International Dictionary of English v.0.48:
Trigon \Tri"gon\, n. [L. trigonum, Gr. ?; ? (see Tri-) + ? a
corner, angle: cf. F. trigone.]
[1913 Webster]
1. A figure having three angles; a triangle.
[1913 Webster]
2. (Astrol.)
(a) A division consisting of three signs.
(b) Trine, an aspect of two planets distant 120 degrees
from each other. --Hutton.
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3. (Gr. & Rom. Antiq.)
(a) A kind of triangular lyre or harp.
(b) A kind of game at ball played by three persons
standing at the angular points of a triangle.
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4. (Zool.) The cutting region of the crown of an upper molar,
usually the anterior part. That of a lower molar is the