"Trigness" is a relatively uncommon word that refers to the state or quality of being trigonous, or having three angles or sides. While there are not many commonly used synonyms for this specific term, there are a number of related words that can be used to convey similar concepts. For example, words like triangular, trigonal, tripartite, and triple can all be used to describe things that have three parts or sides. Additionally, terms like threeness, triplicity, and triad can be used to describe the number three or things that come in sets of three.