No. The compound noun "Sunday school" refers to certain religious education, not merely school held on Sunday. In any event, the proper noun Sunday would be considered a noun adjunct, or attributive noun. In many cases, Sunday would be called an adjectival noun, because it is a form of the prepositional phrase "on Sunday" as in "We will go to church Sunday."
It is neither: it is a proper noun for a holiday.(In 'Easter Sunday' it is a noun adjunct with the proper noun Sunday.)
The possessive form Sunday's is an adjective. The word Sunday in "Sunday paper" is not an adjective but a noun adjunct, because Sunday is not a characteristic of paper.
Because Sunday is a noun, and, by definition, an adjective is used to modify a noun, all that needs to be done to use an adjective in a sentence with the word Sunday is to choose a desired adjective and use it to modify the noun "Sunday". For instance, one could say "A gloomy Sunday." Or, "A busy Sunday."
The proper adjective for George is Georgian.
The proper adjective for Siam is Siamese.
It is neither: it is a proper noun for a holiday.(In 'Easter Sunday' it is a noun adjunct with the proper noun Sunday.)
The possessive form Sunday's is an adjective. The word Sunday in "Sunday paper" is not an adjective but a noun adjunct, because Sunday is not a characteristic of paper.
The proper adjective for southwest is "southwestern."
The proper adjective is Haitian.
The proper adjective for Portuguese is "Portuguese."
Because Sunday is a noun, and, by definition, an adjective is used to modify a noun, all that needs to be done to use an adjective in a sentence with the word Sunday is to choose a desired adjective and use it to modify the noun "Sunday". For instance, one could say "A gloomy Sunday." Or, "A busy Sunday."
Vietnamese is the proper adjective for Vietnam.
The proper adjective for Georgia is Georgian.
The proper adjective for George is Georgian.
Freudian is the proper adjective for Freud.
Mayan is itself a proper adjective.
The proper adjective for Siam is Siamese.