octagon

As a proper noun triangle

is the area comprising the cities of used with "the" except when attributive.

As a noun octagon is

octagon.

As nouns the difference between octagon and square

is that octagon is octagon while square is (geometry) a polygon with four sides of equal length and four angles of 90 degrees; a regular quadrilateral whose angles are all 90 degrees.

As an adjective square is

shaped like a (the polygon).

As a verb square is

to adjust so as to align with or place at a right angle to something else.

As a proper noun octopus

is .

As a noun octagon is

octagon.

As a proper noun calliope

is (greek god) the muse of eloquence and epic or heroic poetry; the mother of orpheus with apollo.

As a noun octagon is

octagon.

As nouns the difference between pentagon and octagon

is that pentagon is pentagon while octagon is octagon.

As nouns the difference between octagon and decagon

is that octagon is octagon while decagon is decagon.

As a noun octagon is

octagon.

As nouns the difference between hexagon and octagon

is that hexagon is a polygon with six sides and six angles while octagon is a polygon with eight sides and eight angles.

As nouns the difference between octagon and octangle

is that octagon is a polygon with eight sides and eight angles while octangle is a geometric figure with eight corners, an octagon.