A polygon with eleven sides and eleven angles.
From Greek 'hendeca-' (eleven, from 'hen' one + 'deca' ten) plus '-gon' (angle). The Greek numerical prefix system allowed mathematicians to name any polygon by its number of sides.
While pentagons and hexagons are everywhere in nature and design, hendecagons almost never appear naturally—this mathematical awkwardness is why you rarely see 11-sided shapes in real life.
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