What is a nine sided shape?

Answer 1

For a 2-dimensinal shape ;-

3; trigon (triangle)

4; tetragon ( quadrilatertal)

5; pentagon

6; hexagon

7; heptagon

8 ; Octagon

9 ; nonagon ( The answer to your question).

10 ;decagon.

For a 3-dimensional object.

4; tetrahedron

5 ; pentahedron

6 ; hexahedron

7 ; heptahedron

8 ; octahedron

9 ; nonahedron

10; deahedron.

The nomenclature is bases on Latin.

Answer 2

A nine sided polygon is called a "nonagon"