circle
Normally the minimum number sides a polygon can have is 3 which is a triangle and probably there is no such name given to a 2 sided polygon.
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 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 8 sided polygon is Octagon.
The name of a 10 sided polygon is Decagon.
The name of a 14 sided polygon is Tetradecagon.
The name of a 99 sided polygon is enneacontaenneagon.
The name of a 18 sided polygon is Octadecagon.