The keyword term "11 sep event" is a noun phrase. The grammatical core, or headword, of this phrase is the noun "event."
In this construction, "event" is the central noun that identifies the subject as a happening or occurrence. The preceding elements, "11 sep" (an abbreviation for the date 11 September), function collectively as an adjectival modifier. This modifier specifies which particular event is being referenced, distinguishing it from all others. The structure follows a common linguistic pattern where a date, location, or other specific identifier modifies a general noun to create a proper name for a historical or significant occurrence.
Recognizing "event" as the main noun is crucial because it establishes the article's focus on the occurrence itselfits characteristics, causes, and consequences. The phrase can function in a sentence as a subject, object, or object of a preposition, allowing for clear and precise statements. This grammatical understanding ensures the article is structured logically around analyzing the specific happening designated by the date.