I somehow ended up in a small argument about the first part of the compound word "fingerprint". The other person insists that the first word "finger" is an adjective, which I cannot agree with. "Fingerprint" is a noun-noun compound word, but my counterpart argues that "finger" is used adjectivally to describe what kind of a "print" it is. I would not say that everything that specifies something or describes something is an adjective. That would just be simplifying some elementary school heuristics for parts of speech…
Now, there certainly are some words that are both nouns and adjectives, such as "cotton", but I doubt "finger" would be one of those.
So, is "finger" in the word "fingerprint" a noun or an adjective? "Fingerprint" is a noun-noun compound anyway. Prove me wrong, maybe I'll learn something.
Best Answer
OED
Noun-noun compound word fingerprint
Just because a noun modifies another noun doesn't make it just an adjective all of the sudden. It remains being a noun that works as an adjective but it's neither of them exclusively. To answer your question whether finger works as an adjective or as a noun in the word fingerprint, I'd say neither of them. Since it's a noun with the function of an adjective but it's not specifically either of them. Or just like Mari-Lou A commented, an adjunct noun if you'd like to give it a name.