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[Earlier, relating to a trigon or triplicity, relating to three angles : Latin trigōnum, triangle; see trigon + -al.]
1. (Mathematics) another word for triangular1
2. (Chemistry) Also: rhombohedral relating or belonging to the crystal system characterized by three equal axes that are equally inclined and not perpendicular to each other
trig•o•nal(ˈtrɪg ə nl)
1. of, pertaining to, or shaped like a triangle; having three angles; triangular.
2. (of a crystal) having threefold symmetry.
Relating to a crystal having three axes of equal length intersecting at oblique angles. This crystal system is considered a subset of the hexagonal system. The mineral quartz has trigonal crystals. Also called rhombohedral. See more at crystal.