Final answer:
In the sentence "It is time to wash the dinner plates," the noun used as an adjective is dinner.
Step-by-step explanation:
In the sentence "It is time to wash the dinner plates," the noun used as an adjective is dinner. Nouns can be used as adjectives to modify other nouns and provide more information about them. In this case, the noun "dinner" is used to describe the type of plates being washed, indicating that they are specifically for dinner.
Learn more about Nouns used as adjectives