Hendecagon
It is an 8 sided polygon - a plane shape bounded by 8 straight lines of equal length. The angles need not be of the same measure.
A polygon is an enclosed plane area whose boundaries comprise straight lines. Two lines in a plane cannot enclose a space. Therefore, there cannot be a two-sided polygon.
It is a closed plane shape bounded by six straight lines.
A quadrilateral is the shape of a 4 sided polygon
A decagon is a closed plane shape bounded by ten straight lines.
A polygon refers to a plane figure that has at least three straight sides and angles. An 18 sided shape is called an octadecagon or octakaidecagon.
It is a plane shape bounded by three straight lines that meet [pairwise] at three distinct vertices.
An octagon is an eight sided shape that has 360 degrees of exterior angles and 1080 degrees of interior angles.
A quadrilateral is a closed plane (2-dimensional) shape bounded by four straight lines that meet at four vertices.
A regular 5 sided pentagon has 5 equal sides and 5 equal interior angles that add up to 540 degrees
A triangle is a shape that has 3 sides and 3 corners. It is a three-sided polygon, which is a plane shape bounded by three straight lines.
A polygon is a plane area bounded by straight lines. Two straight lines cannot define a closed shape. There cannot, therefore by a polygon with only two sides.