non·a·gon
noun/ˈnɒnəɡən/
/ˈnɑːnəɡɑːn/
(geometry)- a flat shape with nine straight sides and nine angles
Topics Colours and Shapesc2九边形;九角形 Word Originmid 17th cent.: formed irregularly from Latin nonus ‘ninth’, on the pattern of words such as hexagon.