Lisbon is the name of a city, a proper noun which should be capitalized. There is no English adjective for a person or thing of or from Lisbon, but the proper adjective in Portuguese is Lisboeta.
Lisbon is a proper noun because it refers to a specific city, the capital of Portugal.
Vietnamese is the proper adjective for Vietnam.
The proper adjective for George is Georgian.
The proper adjective for Siam is Siamese.
No, old is not a proper adjective. A proper adjective is an adjective derived from a proper noun, such as Swiss cheese, Bolivian pottery, Chinese silk, etc.
France is always a proper noun it is never a proper adjective (what is a proper adjective? The adjective is french. I like french food
The proper adjective for Antigua is Antiganantigan
Kuwaiti is the proper adjective for Kuwait.
Oklahoman is the proper adjective for Oklahoma.
Paraguayan is the proper adjective for Paraguay
A proper adjective is a descriptive word derived from a proper noun.Some examples are:Asia (proper noun) - Asian (proper adjective)Brazil (proper noun) - Brazilian (proper adjective)Canada (proper noun) - Canadian (proper adjective)Elizabeth I (proper noun) - Elizabethan (proper adjective)Sigmund Freud (proper noun) - Freudian (proper adjective)George Orwell (proper noun) - Orwellian (proper adjective)Proper nouns and proper adjectives are always capitalized.