polygonometry
/ˌpɒlɪɡəˈnɒmɪtri/ /pəˌlɪɡəˈnɒmɪtri/Mathematics. Now rare
noun
The branch of mathematics that deals with the measurement and properties of polygons in the way that trigonometry deals with those of triangles.
Origin
Late 18th century; earliest use found in New Annual Register 1790. From polygon + -o- + -metry, after French polygonométrie, itself after French trigonométrie.