ˈtrigən ə l adjective
Etymology: Latin trigonalis, from trigonum triangle
1. : of, relating to, or characteristic of triangles : having three angles : triangular
2. : of or relating to a trigon or the trigone
3. : of, relating to, or being the division of the hexagonal crystal system or the forms belonging to it characterized by a vertical axis of threefold symmetry — see trigonal system
• trig·o·nal·ly -nəlē adverb