elevenaside

Elevenaside is a rarely used term that refers to an eleven‑sided polygon. It is not part of the standard mathematical vocabulary, where the shape is typically called a hendecagon or, less commonly, an undecagon. The coinage combines "eleven" with "side" to signal a polygon with eleven edges, but it has no formal definition beyond that equivalence in informal contexts.

In practice, elevenaside appears in puzzles, schematic diagrams, or discussions where a casual name is preferred over the learned terminology. Without additional qualifiers, an eleven-sided figure described as an elevenaside may be irregular or regular; standard geometry fixes a regular eleven-sided polygon as a hendecagon with interior angles of 180*(11−2)/11 ≈ 147.27 degrees and exterior angles of 360/11 ≈ 32.73 degrees when all sides are equal.

The term's lack of formal adoption means it is mostly of historical or colloquial interest. When precision is required, "hendecagon" is preferred.

See also: hendecagon, undecagon, polygon.