The noun 'octagon' is a common noun, a general word for any eight sided figure or object.
A proper noun is the name of a specific person, place, or thing; for example:
Octagon Street, Los Angeles, CA
Club Octagon New York (nightclub)
Junior Optimist Octagon International (youth organization of Optimist International service organization)
proper
As a name of a road , Park Avenue', it is a proper noun, and both words star with a capital letter. However, when used separately, as 'the park, or 'the avenue', they are common nouns and so not need a capital letter.
common
It is a proper noun, because it is the name of a specific thing.
common
A common object that is an octagon is a "stop sign".
equal sides
Yes, the noun 'octagon' is a countable noun, the plural form is octagons.Examples:An umbrella is a common form of an octagon. (singular)The pattern is a series of octagons in traditional colors. (plural)
The most famous is a stop sign.
Length + width = 18 cm so length = 12 cm and width = 6 cm. Presumably the length is the common side so the perimeter of the octagon is 8 x 12 = 96 cm. If the width is the common side then the perimeter of the octagon is 8 x 6 = 48 cm
In general, an octagonal pyramid is a pyramid with an octagon for a base and triangles (which all have a common vertex) for sides. The octagon my or may not be a regular one.
proper
As a name of a road , Park Avenue', it is a proper noun, and both words star with a capital letter. However, when used separately, as 'the park, or 'the avenue', they are common nouns and so not need a capital letter.
common
common and proper
It is a proper noun, because it is the name of a specific thing.
The proper title for the Ultimate Fighting Championship ring girl is an Octagon Girl. One can apply on their official website Octagon Girl to apply and learn more about the position.