Vietnamese is the proper adjective for Vietnam.
The proper adjective for the proper noun 'Celt' is Celtic.Please note that a proper noun and a proper adjective is always capitalized.
Since spice isn't a proper noun, it can't have a proper adjective. The adjective of spice is spicy.
Since writer is not a proper noun, it doesn't have a proper adjective.
Hawaiian is the proper adjective for Hawaii.
The proper adjective for Portuguese is "Portuguese."
The proper adjective for southwest is "southwestern."
The proper adjective for Haiti is Haitian.
Vietnamese is the proper adjective for Vietnam.
The proper adjective for Siam is Siamese.
The proper adjective for Georgia is Georgian.
The proper adjective for Mayan is "Mayan."
The proper adjective for George is Georgian.
Freudian is the proper adjective for Freud.
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.
The proper adjective for Antigua is Antiganantigan
Kuwaiti is the proper adjective for Kuwait.