The most common term is "nonagon", though technically "non-" is a Latin prefix. The purely Greek word for it is "enneagon." But no one really uses this term , so you're safe with "nonagon."
nonagon
Because nonagon means 9 sides
Not a regular nonagon.
A nonagon has nine sides.
A nonagon
"nonagon" is not a prefix.
Nonagon.
a nonagon
A nonagon.
A nonagon is a 2D shape so you cannot make a 3D nonagon!
Only if all nine sides are the same length.