I would call it a 900000-gon. For a large number of side (more than 20), the Greek prefix should only be used for a Greek audience or an audience which you wish to irritate.
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it is called a seven sided shape in Canada
Nonahectmegagongon
A 90 sided shape is called Enneacontagon.
A 128-sided shape is called a hecatoicosioctagon.
An five sided shape is called a Pentagon