nonagon
It is called a nonagon and/or an enneagon. They belong to the greater family of polygons.
ennedagon
Polygons have 3 or more sides, so there are no one sided polygons idiot.
There aren't two sided polygons
Polygons.
multi sided shapes are called polygons
All 10-sided polygons are decagons.
All 4 sided polygons are classed as quadrilaterals.
A 12-sided polygon is called a dodecagon.
Hexagons, assuming they are polygons.
If you mean a 4-sided polygon, then that is a quadrilateral. See related link for more information on polygons.
There are infinitely many of them and they are collectively known as polygons.