The keyword phrase "September 11th attacks 2001" functions grammatically as a proper noun. It operates as a single conceptual unit to name a specific, unique historical event, much like "the Boston Tea Party" or "World War II."
In this construction, the headword is the plural noun "attacks." The components "September 11th" and "2001" are modifiers that specify the date of the event. They function adjectivally, answering the question "Which attacks?" The entire phrase is capitalized and treated as a singular name, distinguishing this specific series of coordinated terrorist attacks from any other attacks.
Recognizing the phrase as a proper noun is crucial for syntactic analysis. It allows the entire term to act as a subject, object, or object of a preposition within a sentence. For instance, in "The September 11th attacks 2001 altered international relations," the phrase serves as the subject. This classification is fundamental for information retrieval, indexing, and cataloging, as it ensures the event is treated as a distinct entity rather than a simple combination of a date and a common noun.
