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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?