This stop sign is an octagon.
The definition of an octagon is an eight-sided, eight-angled figure.
An example of an octagon is the shape of a stop sign in the US.
a plane figure with eight angles and eight sides
Origin of octagonClassical Latin octagonum ; from Classical Greek oktag?nos, eight-cornered: see octa- and amp; -gon
A polygon with eight sides and eight angles.
Origin of octagonLatin octag&omacron;non, from Greek oktag&omacron;non, from neuter of oktag&omacron;nos, octagonal : okta-, octo- + -g&omacron;nos, angled; see –gon.