Definition of nonagon noun from the Oxford Advanced Learner's Dictionary



BrE BrE//ˈnɒnəɡən//
; NAmE NAmE//ˈnɑːnəɡɑːn//
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a flat shape with nine straight sides and nine angles Word Origin mid 17th cent.: formed irregularly from Latin nonus ‘ninth’, on the pattern of words such as hexagon.
See the Oxford Advanced American Dictionary entry: nonagon