Sesquinonagintagon

Sesquinonagintagon is a coined term representing a specific angular measure of 135 degrees, derived from the combination of the Latin prefix “sesqui-” meaning one and a half, the Latin word “nonaginta” meaning ninety, and the Greek suffix “‑gon” meaning angle. The term is used primarily in mathematical literature and geometry teaching contexts where it is helpful to highlight compound fractional angles derived from whole degrees.

The construction of the word follows a pattern seen in other hybrid mathematical terms such as decagon (ten‑gon) or centagon (hundred‑gon). By embedding the fractional prefix “sesqui‑” it indicates that the angle is one and a half times a base value of 90 degrees. The notation is typically written in uppercase in scientific texts as S E S Q U I N O N A G I N T A G O N to emphasize its constructed nature.

While sesquinonagintagon has not been incorporated into formal mathematical dictionaries, it appears in puzzle books, early geometry lessons, and educational software as a mnemonic for remembering the value of the commonly used digital compass angles. The term’s specificity allows it to serve as a concise reference in problem statements that require an intermediate angle between the standard right angle and the conventional obtuse angles typically expressed as 120 or 150 degrees.