Main Difference
The main difference between Octagon and Hexagon is that the Octagon is a polygon with eight sides and Hexagon is a polygon with six sides.

Octagon
In geometry, an octagon (from the Greek ὀκτάγωνον oktágōnon, “eight angles”). Is an eightsided polygon or 8ton
A regular octagon has Schläfli symbol {8} and can also be constructed as a quasiregular truncated square, t{4}, which alternates two types of edges. A truncated octagon, t{8} is a hexadecagon, t{16}.

Hexagon
In geometry, a hexagon (from Greek ἕξ hex, “six” and γωνία, gonía, “corner, angle”) is a six sided polygon or 6gon. The total of the internal angles of any hexagon is 720°.

Octagon (noun)
A polygon with eight sides and eight angles.

Octagon (noun)
The UFC.

Hexagon (noun)
A polygon with six sides and six angles.

Octagon (noun)
a plane figure with eight straight sides and eight angles.

Octagon (noun)
an object or building with an octagonal plan or cross section.

Hexagon (noun)
a plane figure with six straight sides and angles.