The keyword term "september 11th coin certificate" is a noun phrase. The main point and grammatical subject of this phrase is the head noun, which is the final word: certificate. This establishes that the primary topic of discussion is a document, not the event or the coin itself.
In this construction, the preceding words function as modifiers, creating a specific type of compound noun. The word `coin` is a noun adjunct, acting as an adjective to describe the nature of the certificate (i.e., a certificate related to a coin). The term `september 11th` is another noun phrase used attributively, modifying `coin` to specify its commemorative theme. The grammatical hierarchy is that "september 11th" modifies "coin," and the resulting unit "september 11th coin" modifies "certificate."
For the purpose of writing an article, recognizing "certificate" as the main point is critical. It dictates that the article's focus should be on the certificate itselfits authenticity, the information it contains, its physical characteristics, its role in numismatics, or its value as a collectible document. The coin and the date are essential context, but the central subject is the official paper that accompanies and validates the coin.
