hendecagon

This term is primarily used in geometry and architectural design to describe a specific eleven-sided polygon. Because it is a highly specialized mathematical term, it is rarely encountered in casual conversation and is typically reserved for technical, academic, or professional contexts.

While the word is countable, it is frequently used in the singular when referring to the abstract geometric concept of the shape itself. In practical application, it is often contrasted with more common polygons like the hexagon or octagon to emphasize a specific, unusual symmetry.