Ravenclaw House: One of the four houses of Hogwarts, extolling the virtues of wisdom and friendship. Its symbol is an eagle, and its colors are blue and silver. Attempting to combine this with the versions of its badge appearing in the movie and on merchandise gives Azure, an eagle displayed, wings inverted, argent, which really doesn't resemble either of those versions. The house ghost is the Grey Lady.
Etym: Invented. The raven is a symbol of wisdom in Norse mythology.
Remembrall: An item resembling a clear marble, which flashes red when the owner has forgotten something. It is unable to indicate what has been forgotten, though.
Reparo: An incantation to fix minor damage.
Etym: Latin, "I repair". Imperative: repare "be repaired".
Restricted Section: A part of the Hogwarts library open only to faculty, advanced students of Defense Against the Dark Arts, and other students who can get a teacher's permission. Naturally, this is where all the really interesting and useful books are kept.
Rise and Fall of the Dark Arts, The: A book in the Hogwarts library.
rock cakes: A type of fruitcake, meant to be hard only on top but frequently ending up hard all the way through.
Ron Weasley [Ronald]:
Etym: From a compound of the Old English words regen and weald, both of which mean "power, force, might".
Ronan: One of the centaurs living in the Forbidden Forest.
Etym: Gaelic for "seal".
Rubeus Hagrid: Etym: From the Latin for "reddish".