The keyword phrase "patriots day massachusetts mail delivery" functions as a noun phrase. The main point or head of this phrase is the compound noun "mail delivery". This term identifies the central subject of the article.
In this grammatical structure, "delivery" is the core noun, specifying the action or process being discussed. "Mail" is a noun adjunct, which is a noun used as an adjective to modify "delivery" and specify its type. The terms "Patriots Day" and "Massachusetts" are also noun adjuncts (specifically, proper nouns used adjectivally). They modify the head noun "mail delivery" by providing specific context, answering the questions of "when" and "where."
Determining that "mail delivery" is the primary noun is crucial. It establishes that the article's core subject is the service of delivering mail, not the holiday or the state itself. The other words simply act as limiters, narrowing the article's focus to the status of this specific service at a particular time and place.
