Adjectives are words that describe nouns and pronouns.
Proper nouns are nouns that name specific people, places, things, or ideas. Think of proper as meaning specific.
- Notice that proper nouns always begin with a capital letter.
- Examples of proper nouns: America, English, Paris
Proper adjectives are adjectives that are formed from proper nouns.
Most proper adjectives identify people, places, languages, or groups.
- Examples of proper adjectives: American cars, English grammar, Parisian scarf
Notice that proper adjectives are still performing the job of an adjective: They are all describing nouns.
Edited from source: English Grammar Revolution/Proper Adjectives