Just calling it a "1000-sided shape" is fine. It is too much trouble to search for fancy name for figures with many sides.
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A 1000 sided shape is called a Chiliagon.
a 10000 sided shape is a myriagon some people call polygons: 10-gon 100-gon 1000-gon and so on
millotigon
An 11 sided shape is an Eptogon
A nine sided shape or polygon is called a nonagon.