The proper noun Korea (a region, two countries) has the proper adjective Korean (adjective and demonym).
korean
The proper adjective for George is Georgian.
The proper adjective for Siam is Siamese.
The proper adjective for Antigua is Antiganantigan
Kuwaiti is the proper adjective for Kuwait.
korean
Korean
Yes, it can be, used as the proper adjective for the proper noun Korea (Korean peninsula, Korean food). Korean is also a noun, for the language or as a demonym for a person from Korea.
The proper adjectives are:KoreanPolishAlaskanBelgianSwedishFrenchRussianCubanPeruvianIndian
The proper noun North Korea (a country) has the proper adjective North Korean. It is also a noun for a person from that country (a demonym).
The proper adjective for southwest is "southwestern."
The proper adjective is Haitian.
The proper adjective for Portuguese is "Portuguese."
Vietnamese is the proper adjective for Vietnam.
The proper adjective for George is Georgian.
The proper adjective for Siam is Siamese.
Mayan is itself a proper adjective.