What does endecagon mean?
An endecagon is a polygon with eleven sides and eleven interior angles. Like all polygons, it may be regular — with all sides and angles equal — or irregular. The term is a less common alternative to 'hendecagon', the form preferred in most mathematics texts, though both words derive from the same Greek elements meaning 'eleven' and 'angle'. Endecagons appear rarely in everyday life compared with triangles, squares, or hexagons, but they do occur in design contexts such as coins, tiles, and architectural plans where a many-sided but not-quite-circular shape is wanted. Because constructing a regular eleven-sided polygon exactly requires more than compass and straightedge alone, it has long interested mathematicians alongside other polygons that resist classical construction. The word belongs to formal and educational registers and will most often be met in geometry lessons or reference works.
nounA polygon with eleven sides and eleven angles.
- A plane figure with eleven sides and eleven angles.
"The coin's unusual shape was an endecagon, its eleven straight edges catching the light."
"The students struggled to construct an endecagon with ruler and compasses."
"The garden's central bed was laid out as an endecagon, each of its eleven sides planted with a different herb."
Standard plural; used when referring to multiple such figures.
"The textbook illustrated both regular and irregular endecagons."
An eleven-sided polygon is so rare that mathematicians couldn't agree on what to call it — 'hendecagon' won, but 'endecagon' survives as its stubborn synonym.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of endecagon
The word comes from the Greek roots 'hendeka', meaning eleven, and 'gōnia', meaning angle or corner, entering English through scholarly Latin usage. The variant form with initial 'e-' reflects a common alternation in how Greek numerals were adapted into English spelling. Its sibling terms — pentagon, hexagon, heptagon, octagon, decagon — all share the same '-gon' suffix from the same Greek root.
How endecagon is actually used
'Endecagon' is considerably rarer than 'hendecagon', which is the standard mathematical term for an eleven-sided polygon. It is chiefly encountered in technical or educational contexts.
Easily confused with endecagon
Both name an eleven-sided polygon; 'hendecagon' is built from Greek roots and is the more common term, while 'endecagon' uses a Latinized variant of the Greek prefix.