Ah, what a lovely question. The proper noun "Panama" becomes a common noun when we refer to it as a type of geographical feature called an isthmus. Just like how we can call a specific painting "art," we can refer to Panama as an isthmus. Keep exploring the beauty of language, my friend.
A common noun for the proper noun "Panama" would be "country." Common nouns are general, non-specific terms used to refer to a class of entities, in this case, a geographical area. "Panama" is a proper noun because it specifically names a particular country in Central America.
The compound noun 'Suez Canal' is a proper noun, the name of a specific place.
"Park Avenue" is a proper noun, because it is a place. Proper nouns like this should always be capitalized.
Common
A proper noun is the name of a specific person, place, or thing. A proper noun for the common noun 'canal' is the name of a canal, such as the Panama Canal, The Suez Canal, or the well known street in New York City, Canal Street.
It is a proper noun, because it is the name of a specific thing.
proper
Proper noun
it's a common noun. a proper noun would be Spider-Man.
Pencil proper or common noun
Proper noun or common noun
The noun cassette is a common noun.
a common noun?