Part of speech?

They want you to write two sentences using the word "key." In one of the sentences, "key" should be a noun--the name of a person, place, or thing.

In the other sentence, they want you to use the word "key" as an adjective, a word which describes a noun.

I won't do anybody's homework for them, but here's another word which can be a noun or adjective, "down."

The baby chicken was covered in yellow down.
I put on my down jacket.