In grammatical terms, "Patriots' Day" functions as a proper noun. It is the specific, capitalized name of a particular civic holiday, which distinguishes it from a common noun like "holiday" or "celebration." As a proper noun, it identifies a unique entity.
The term is technically a compound noun phrase. The word "Patriots'" is a possessive noun that acts as an adjective modifying the core noun, "Day." However, the entire two-word phrase "Patriots' Day" operates as a single, indivisible unit to name the specific event. Its function is analogous to other named days, such as "Memorial Day" or "Independence Day," where the combination of words forms a singular proper noun that serves as the official title.
Recognizing "Patriots' Day" as a proper noun dictates its correct usage in writing. It requires capitalization for both words. Within a sentence, it can serve any function that a noun can, such as the subject ("Patriots' Day is a state holiday in Massachusetts."), a direct object, or the object of a preposition ("The Boston Marathon is held on Patriots' Day."). This classification is essential for maintaining grammatical accuracy and clarity.
