An apeirogon.
Apeirogons are degenerate polygons that probably appear as never ending straight lines
Circle.
apeirogon
icosihenagon= 21-sided polygon icosihenagon= 21-sided polygon
I would just call it an "800-sided polygon."
The name of a sided polygon is Octaconpentagon.
The name of a 18 sided polygon is Octadecagon.
The name of a 11 sided polygon is Hendecagon.
The name of a 8 sided polygon is Octagon.
The name of a 33 sided polygon is riacontakaitrigon.
A 10-sided polygon is called a decagon.
The name of a 262 sided polygon is dihectrahexacontadigon.
The name of a 1999 sided polygon is Chiliaenneahectaenneacontaenneagon.