A nonagon or enneagon is a nine- sided polygon or 9-gon. Nonagon = Nona + gon where Nona means nine and gon means sides.
A 9-sided "circle" is an nonagon or enneagon.
a chord. The chord that passes through the center of the circle has a special name: the diameter.
Circle mobius strip
There is no specific name for such an angle.
You just hold down alt and press 9 on the right side ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○
nonagon
Being half of the circumference of a circle, a semi circle has one side
The circumference of a 9 circle is: 28.3
Nonagon, or enneagon.
If the diameter of a circle is 9 the circumference is: 28.3
If a circle has a circumference of 9, the diameter is: 2.864
A square whose diagonal is the diameter of the circle. So, if it is a circle with diameter 18 units then the diagonal of the square is 18 units and so its side is 9*sqrt(2) = 12.7 units.