The keyword term "US Sept 11" functions as a proper noun. It operates as a single, cohesive unit to name a specific, unique historical event: the terrorist attacks that occurred in the United States on September 11, 2001. As a proper noun, it identifies a singular entity, much like the names "World War II" or "the Great Depression."
This grammatical classification is derived from the phrase's function within a sentence. Despite being composed of multiple wordsan abbreviation for a country ("US"), an abbreviation for a month ("Sept"), and a number ("11")the combination acts as a compound noun. It serves as the subject of a verb (e.g., "US Sept 11 changed foreign policy.") or the object of a verb or preposition (e.g., "The article analyzes US Sept 11."). The term does not modify another word, which would make it an adjective, nor does it express an action, which would make it a verb.
Identifying "US Sept 11" as a proper noun is the crucial step because it establishes the event itself as the central subject of the article. This allows for direct and unambiguous statements about the event, its causes, and its consequences. Grammatically, it provides a stable anchor for the entire discourse, ensuring that all subsequent analysis, data, and discussion refer back to this specific, named entity.
