Here's why:
* It refers to a group: A dossier is a collection of documents, often related to a specific topic or person.
* It's singular in form: You would say "the dossier" or "this dossier," not "the dossiers."
* It represents the whole: The word "dossier" encompasses all the individual documents within it.
However, it's important to note that "dossier" doesn't always function like a true collective noun:
* It often carries a specific meaning: "Dossier" implies a structured collection of documents, often for investigative or official purposes.
* It's not always interchangeable with other collective nouns: You wouldn't say "the dossier of documents" because "dossier" itself implies a group of documents.
So, while "dossier" can be considered a collective noun for documents, it's more nuanced than some other collective nouns like "flock" or "team."