The word "triagonal" refers to something that has three angles or corners. Synonyms for this word include triangular, trilateral, and triquetrous. Triangular is probably the most commonly used synonym and refers specifically to objects or shapes with three straight sides and three angles. Trilateral is similar but can also be used to describe relationships between three parties or organizations. Triquetrous is a less common synonym and refers to something that has three prominent projections or ridges. Other less common synonyms might include trifid, which means something that is divided or split into three parts, and trihedral, which refers specifically to a solid object with three flat faces that meet at straight edges.