The keyword term "September 11th US" functions grammatically as a proper noun phrase. It acts as a single unit to name a specific and unique historical event: the terrorist attacks that took place in the United States on September 11, 2001. As a proper noun, it refers to a particular entity and is capitalized accordingly.
This phrase is a compound construction. The core component, "September 11th," has transcended its original meaning as a calendar date to become the common name for the event itself. The second component, "US" (an abbreviation for the proper noun United States), functions here as a noun adjunct or an adjectival noun. Its role is to modify "September 11th," specifying the geographic and political context. The two words combine to create a more precise identifier, distinguishing this event from other significant events that may have occurred on that date elsewhere in the world.
For the purpose of an article, establishing this term as a proper noun is the crucial main point. This classification dictates its usage in sentences, where it can act as a subject, an object, or the object of a preposition. Treating "September 11th US" as a singular noun ensures semantic clarity and precision, allowing the article to consistently refer to the specific event as a well-defined topic of discussion.
