Meaning

noun a three-sided polygon

noun (astrology) one of four groups of the zodiac where each group consists of three signs separated from each other by 120 degrees

noun a triangular lyre of ancient Greece and Rome

originFrom Ancient Greek τρίγωνον (trígōnon, “triangle”), neuter substantive of τρίγωνος (trígōnos, “three-sided”), from τρεῖς (treîs, “three”) + γωνία (gōnía, “bend, angle”). Equivalent to tri- + -gon. Doublet of trigone and trigonon.

Etymology from Wiktionary, CC BY-SA 3.0