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The Collaborative International Dictionary
Trigonal

Trigonid \Tri"go*nid\ [Webster 1913 Suppl.] Trigonal \Trig"o*nal\, a. Having three angles, or corners; triangular; as, a trigonal stem, one having tree prominent longitudinal angles.

Wiktionary
trigonal

a. symmetrically triangular

WordNet
trigonal

adj. having three-fold symmetry [syn: rhombohedral]

Usage examples of "trigonal".

Outwardly this formation resembled quartz in that it crystallized in the trigonal trapezohedral class of the rhombohedral subsystem of hexagonal symmetry.