Circle.
apeirogon
An infinite-sided shape is called a "circle" in the context of geometry, as it can be seen as a polygon with an infinite number of sides. More formally, in the realm of mathematics, a shape with an infinite number of sides is often referred to as a "apeirogon." An apeirogon is a polygon that extends indefinitely, having an infinite number of vertices and edges.
The name of a 12 sided polygon is Dodecagon.
A 8 sided polygon is called a octagon.
name of 4000 sided polygon
The name of a 10 sided polygon is Decagon.
The name of a 9 sided polygon is Nonagon.
The name of a 19 sided polygon is enneadecagon.
The name of a 17 sided polygon is Heptadecagon.
The name of a 15 sided polygon is Pentadecagon.
The name of a 7 sided polygon is Heptagon.
The name of a 8 sided polygon is Octagon.