The keyword phrase "US Patriot Day" functions as a proper noun. It is the specific name of a designated annual observance in the United States.
In a grammatical breakdown of the phrase, "Day" is the head noun. The terms "US" (an abbreviation for United States) and "Patriot" act as adjectival modifiers. "US" specifies the national context, while "Patriot" describes the nature of the observance. When combined, these components form a single, multi-word unit that names a unique event, which is the defining characteristic of a proper noun.
Recognizing "US Patriot Day" as a proper noun is essential for correct usage. This classification dictates that the phrase must be capitalized. Furthermore, within a sentence, it functions as a single noun and can serve as a subject, object, or object of a preposition. For example, in the sentence, "Americans observe US Patriot Day," the phrase acts as the direct object.
