What part of speech is the word hair in 'hair spray'? [duplicate]

Question

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Consider the following sentence as an example. I used some hair spray. What part of speech is hair? Intuitively, I want to say it's an adjective modifying spray since hair spray is two separate words and not a compound noun. Hair spray however, as paired nouns, is something that we've decided to call a thing suggesting it might be a noun or maybe some other part of speech as part of a noun cluster (if such a thing exists). A dictionary entry for hair does not describe hair as an adjective. I can think of several more examples like this:

money order, pocket comb, tip money.

Are money, pocket and tip adjectives or something else?

Answer 1

Compound nouns is when a noun forms a new noun when modified by either an adjective or, as in this case, by a noun. You can be more specific saying that it is a compositional compound noun, as opposed to a non-compositional noun phrase like red herring. You compose the meanings of hair and spray and can deduce the meaning of the resulting noun phrase hair spray. This is in contrast to red herring, which is neither red nor a herring.

It is also an spaced compound. The two nouns are written separate. It is a descriptive endocentric compound, since hair is modifying spray and the meaning ends up being a type of spray.