Is the dictionary wrong? Here's an example; you decide (use the rules of grammar and common human natural-language sense, not the rules of logic, which rely entirely on antecedent definitions):
The United States, England and Canada have a lot in common. The former, for example, used to own the other two!
Former here seems to me to be a noun. But according to m-w.com and wiktionary.org, this can't be true because it is just an adjective! How can this be?