What does decagon mean?
A decagon is a two-dimensional geometric figure bounded by ten straight sides, forming ten interior angles. When all its sides are of equal length and all its angles equal, it is described as a regular decagon, in which each interior angle measures 144 degrees. The word belongs primarily to mathematics and appears most often in geometry lessons, architectural descriptions, and discussions of design, where ten-sided shapes occasionally feature in floor plans, coins, and decorative motifs. Like other polygon names — triangle, pentagon, hexagon, octagon — it combines a Greek numeral prefix with the suffix '-gon', meaning 'angle' or 'corner'. Although precise in meaning, decagon is not part of casual everyday speech; it signals a technical or educational context. Its usefulness lies in naming a specific shape that would otherwise require cumbersome description, making it a staple of mathematical vocabulary.
nounA plane figure with ten straight sides and ten angles.
- A polygon with ten sides and ten interior angles; in a regular decagon all sides and angles are equal, each interior angle measuring 144 degrees.
"The courtyard was laid out as a decagon, with ten identical walls meeting at ten corners."
"Students learned to construct a regular decagon using only a compass and straightedge."
"The coin was struck in the shape of an irregular decagon to distinguish it from round currency."
Standard English plural; used when referring to multiple ten-sided figures.
"The tessellation exercise compared how hexagons, octagons, and decagons fit together on a flat surface."
The prefix 'deca-' means ten in Greek — the same root that gives us decade, decimal, and December, which was once the tenth month of the Roman year.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of decagon
Decagon derives from the Greek 'dekagōnon', formed from 'deka', meaning 'ten', and 'gōnia', meaning 'angle' or 'corner'. The word entered English via Latin in the sixteenth century, when classical Greek mathematical vocabulary was being absorbed into European scholarship. It shares the Greek root 'deka-' with words such as decimal, decade, and decimate, all of which carry the sense of ten.
Related word forms
How decagon is actually used
Decagon is a technical term used mainly in geometry and mathematics education. It is neutral in register but rare in everyday conversation outside classroom or design contexts.
Easily confused with decagon
A dodecagon has twelve sides, whereas a decagon has exactly ten.
A nonagon has nine sides and nine angles, one fewer than a decagon's ten.