Noun adjuncts

Even an old dog can learn something new.

I have taught for years that the noun coming before another noun and describing the second noun is simply a noun acting as an adjective. But there is a name for this noun. It is a noun adjunct.
Here is what I am talking about.

In the phrase raisin bread, the word raisin is a noun adjunct. It is a noun describing a second noun, bread.

This differs from a compound noun like toothbrush which is two nouns combined to form one word.

Although noun adjuncts will not be on any tests that I give, it is nice to learn something new. By the way, I checked my old grammar books, and there is nothing in them about noun adjuncts, so I guess I have an excuse for my ignorance.