I would call it a "ten-thousand sided polygon". Inventing (or memorizing) fancy names for all sorts of polygons, especially those with many sides, really doesn't make much sense.
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Chillagon = 1,000 sides
Myriagon = 10,000 sides
Decakismyriagon = 100,000 sides
Megagon = 1,000,000 sides
A polygon with 6 sides is called a hexagon.
A polygon is a closed figure bounded by sides only. Triangle is the polygon of 3 sides and 3 vertices.
HexagoN
Two adjacent sides of a polygon will meet at a vertex. End points of any other pairs of sides do not have a specific name.
It is enneadecagon (or enneakaidecagon or nonadecagon).