A regular hexagon
A hexagon with 6 congruent sides is a regular hexagon
A circle can.
A hexagon based pyramid.
Is an irregular hexagon.
Yes! All six sides of a hexagon are congruent. It doesn't have to have all sides congruent. A hexagon only needs six sides to be a hexagon.
An hexagonal based pyramid would fit the given description
yes it is
If the hexagon's sides and angles are congruent, then it a regular hexagon.
It can have two congruent sides but does not have to.
Partitioning a general hexagon into 18 congruent parts is normally impossible.