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.