Decagon

The story of the word

Greek geometry named polygons by their corners rather than their sides, so a ten-sided shape is officially a ten-angled one. The same γωνία sits inside diagonal, which is the line running through from angle to angle, and inside goniometer, an instrument for measuring angles. Δέκα also gave Latin decem and so December, once the tenth month.

How it travelled

Ancient Greek → Latin → English

First recorded

17th century