It is an adverb. It adds description to verbs, not nouns.

Adjectives describe (or modify, if you prefer) nouns. So, you can say, for example, “he is a happy cat”. Happy is the adjective.

Now, let’s take quite. You can say, “The cat is quite tired”. Quite is not describing the cat; it is describing the tired. You can also see that quite is easily replaced with other adverbs, such as “very” or “thoroughly”: “the cat is very tired”; “the cat is thoroughly tired”.

Therefore, quite is an adverb.

The mouse is quite small.

If this or another answer here proves helpful in your research, you can encourage good answers by choosing one answer as the “best answer.”

Cheers,

Bruce

David above almost had it but didn’t realize that in his example “quite” was actually modifying “small” not paycheck. In my day, our teachers made us diagram sentences. It really helped.

To be an adjective, it would have to be used like this “She was quite a woman!”