An adjective is a word that tells us more about a noun. (By "noun" we include pronouns and noun phrases.)
An adjective "qualifies" or "modifies" a noun (a big dog).
Adjectives can be used before a noun (I like Chinese food) or after certain verbs (It is hard).
We can often use two or more adjectives together (a beautiful young French lady).
the richest, the most excitinggradability quiz)
nouns as adjectives
coffee cup, bus station, research centre