A hemisphere is a 3-d shape and so does not have a name as a 2-d shape.
2-d sections of a hemisphere can be circles, semicircles, or sections of circles, depending on the inclination of the intersecting plane.
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A 2D shape with 9 sides is called a Nonagon.
Hexagon
A pentagon
Octagon
A '2d' ( 2-dimensional) shapoe is a straight line, or a polygon.