A proper noun is the name of a person or a place. Proper nouns are always capitalized.
Sometimes a proper noun is used to modify a noun. When that happens, the proper noun becomes an adjective. We call it a Proper Adjective.
Here are some proper nouns: German, Sunday, America
German is the name of a language and a nationality.
Sunday is the name of a day of the week.
America is the name of a country.
Each of these proper nouns becomes an adjective when it is placed in front of another noun to modify that noun.
My German teacher showed us a movie.
The proper noun German has become a modifier for the noun teacher.
What kind of teacher? A German teacher.
We ate Sunday dinner at Grandma’s house.
The proper noun Sunday has become a modifier for the noun dinner.
What kind of dinner did we eat? Sunday dinner.
I see the American flag.
The proper noun America has been changed slightly to American. American is a modifier for the noun flag. What kind of flag is it? An American flag.
Many country names get changed slightly when they are used as proper adjectives. Look at these examples. The first word is a proper noun. The second word is a proper adjective.
China > Chinese
Italy > Italian
Mexico > Mexican
I went to China and had a Chinese fortune cookie.
I visited Italy. I enjoyed the Italian food.
In Mexico, the Mexican people speak Spanish.
Proper nouns are names for people and places. A proper noun becomes a proper adjective when it is placed in front of a noun to modify that noun. Proper adjectives are always capitalized.