Adjectival phrase. It does not indicate “characterized by propriety” (as in proper behavior) but rather fits this subsidiary OED definition of proper: “Strictly or accurately so called; in the strict use of the word; genuine, real.” The OED has surprisingly few citations, the first notable one coming from Ann Thwaite’s 1984 biography of Edmund Gosse: “He had worked with magnifying slides but he had never had a proper microscope.” Three years later, more to the point of Britishisms, came a book called A Proper Tea: An English Collection of Recipes.
Help me out here. I can’t put my finger on it, but there is something very British about thinking about or referring to this quality. Americans don’t generally care about whether a particular thing satisfies all the attributes of its category, only whether or not it works or is a good buy. They didn’t used to, that is. Now they are all over “a proper.”
Our distant ancestors probably did not have a proper breakfast when they woke up in their caves, so they gorged whenever they made a kill. (Marian Burros, New York Times, December 18, 2002)/Now that Anderson Cooper has come out of the closet about his admiration for Nicole “Snooki” Polizzi, it’s only fitting that they go out on a proper date. (TVGuide.com, September 15, 2011)