Other forms: decagons
A decagon is a closed shape with ten sides and ten angles. Your geometry teacher would also tell you that a decagon is a polygon.
The word decagon comes from Greek roots, deka, or "ten," and gōnia, "angle or corner." Any ten-sided shape can be called a decagon, whether it's a street sign or the doodle you draw in your notebook during math class. Speaking of math class, in geometry you may learn that a "regular decagon" is one with sides that are all equal to each other and with internal angles that all measure 144 degrees.