Well, darling, a 100000000 sided polygon is called a hectaenneacontagon. It has 100,000,000 sides and 100,000,000 angles. It's a beast of a shape, but hey, at least now you know what to call it when you see one!
a hectamegagon
A 10-sided polygon is a decagon.
A pentagon and a quadrilateral, respectively.
A ten-sided polygon is called a decagon.
The name of a 10 sided polygon is Decagon.