What is a proper adjective?
An adjective, typically capitalized, derived from a proper noun.
You probably are familiar with proper noun: the special nouns in the English language that are privileged enough to have their first letter capitalized. These are the nouns that refer to specific things, places, or people. For example, writer is a regular noun, but Shakespeare is a proper noun.
The noun country is regular, but Canada is a proper noun. Now, proper nouns are in fact the origins for proper adjectives. If Shakespeare is the proper noun, Shakespearian is the proper adjective. If Canada is the proper noun, Canadian is the proper adjective. Just like proper nouns, proper adjectives are capitalized, too.
Taken from: grammar.yourdictionary.com
A specific, capitalized adjective obtained from a corresponding proper noun
Proper nouns are capitalized, specific nouns that denote a place, person, idea, activity, or object.
Examples of proper nouns:
Examples of proper adjectives:
Christian (can also be a proper noun, depends on how it is used)
Examples of sentences with proper adjectives:
My Christian friend lives in California. (Christian is describing the common noun friend.)
The Canadian athlete trains hard everyday. (Canadian is describing the common noun athlete.)