A plane figure with ten straight sides and angles.
- ‘Decagons Here is a decagon - a 10-sided regular polygon with all its angles equal and all its sides the same length - which has been divided into 10 triangles.’
- ‘A thin diamond and a thick one form an endlessly interlocking field of five-pointed stars and decagons, sort of like a mildly psychedelic bathroom tile.’
- ‘How much more sacred than our triangle would be a square, a pentagon, a decagon, a figure with a hundred sides?’
- ‘You can buy 10-sided dice (bi-pyramids) or else you can cut out a decagon (a 10-sided polygon with all sides the same length) from card and label the sides from to 9.’
Mid 17th century: via medieval Latin from Greek dekagōnon, neuter (used as a noun) of dekagōnos ten-angled.