Also 7 -one. [f. Gr. ἐννέα nine + γωνία angle.] A plane figure with nine angles. Hence Ennegonal a., having nine angles.

1

1660.  Barrow, Euclid, IV. xi. Then is AB the side of Enneagone.

2

1721–1800.  in Bailey.

3

1817.  H. T. Colebrooke, Algebra, 92. The regular pentagon, heptagon, and enneagon.

4