A heptagon is a polygon that has seven sides.
A heptagon is a geometric figure with seven sides.
triangle .. ^^
circle
Dekagon.
A heptagon is a seven-sided closed polygon.
It's called an internally contradictory definition. "Quadrilateral" means a figure with four sides. A figure with no sides is not a quadrilateral.
A pyramid with a base that has seven sides.
A hendecagon.
A polygon.
A quadrilateral.
An octagon.