Definition of nonagon in English:

nonagon

noun

  • A plane figure with nine straight sides and nine angles.

    • ‘The room is shaped as a large nonagon, its sheer walls, a flat metallic grey, rising almost two stories up and curving into a dome.’
    • ‘What's the perimeter of a nonagon whose sides are each twice the length of the side of a square whose area is 16 square units?’

Origin

Mid 17th century: formed irregularly from Latin nonus ninth, on the pattern of words such as hexagon.

Pronunciation:

nonagon

/ˈnɒnəɡ(ə)n/