What is a 69 sided polygon called?

A 69-sided polygon is called a hexacontakaienneagon - derived from the prefix for 60 hexacontakai and the prefix for 9 ennea.

Naming a polygon by its number of sides requires that we know the appropriate Greek prefixes along with some rules for their use.

For polygons with 3 through 20 sides, simply add "gon" to the prefixes at the right (although a trigon is more commonly called a triangle and a tetragon, a quadrilateral).

For more than 20 sides, we "construct" the name by using so-called combining prefixes.

To "construct" a name, we start with the prefix for the tens digit, follow it by "kai" (the Greek word for "and"), then follow it with the prefix for the units digit, and finally add "gon."

Example: A 35-sided polygon is called a "triacontakaipentagon" {30 (triaconta) + and (kai) + 5 (penta) + gon)}.

For numbers from 100 to 999, we need one more combining prefix and another rule.

To "construct" the name, we start with the prefix for the hundreds digit taken from the "Ones Digit" table above, follow it by "hecta" (100) then proceed as before.

Example: A 672-sided polygon is called a "hexahectaheptacontakaidigon" {600 (hexa + hecta) + 70 (heptaconta) + and (kai) + 2 (di) + gon)}.