The keyword term is a noun phrase. Its main part of speech is noun, as determined by the final word, "scene," which is the head of the phrase. The entire three-word unit functions grammatically as a single noun, referring to a specific type of setting or depiction.
In this construction, "patriot" and "day" function as noun adjuncts (or attributive nouns). They act like adjectives to modify the subsequent noun. Specifically, "patriot" modifies "day" to designate the specific holiday, and the resulting compound "Patriot Day" then modifies the head noun "scene" to describe its context or subject matter.
For the purpose of writing and grammatical analysis, the entire phrase should be treated as a single conceptual unit that can act as the subject, object, or complement in a sentence. For example, in the sentence "The documentary featured a solemn patriot day scene," the phrase serves as the direct object of the verb "featured."
