Etym: The Middle English spelling of abbot, just the thing to go along with the Fat Friar.
Adalbert Waffling: Etym: No etymology found. Name of a bishop of Hamburg-Bremen, and a Lombard king of Italy.
Adrian Pucey: Etym: From Latin Hadrianus "of the Adriatic", name of an emperor and several popes.
Adventures of Martin Miggs, The Mad Muggle, The: A comic book series that Ron reads.
Agrippa (PS ch. 6): Henrich Cornelius Agrippa von Nettesheim, at various times the secretary to Charles V, physician to Louis of Savoy, theologian, military entrepreneur, philosopher, orator, public advocate (discharged for defending an accused witch) and expert on occultism. His De occulta philosophia was one of the biggest influences on the Renaissance concept of magic, particularly Kabalism, and his writings and fame made him a figure in early versions of the Faust legend.
Featured in the Famous Witches and Wizards series of trading cards.
akashic record: A New Age concept derived from Hindu occultism. An alternate dimension or invisible energy in which psychic vibrations of every object and event, past, present, and future, are stored, thus providing a mechanism for clairvoyance. I chose this name because all the good relevant ones were taken, and in the faint hope that perhaps I have managed to make a forward reference.
Alberic Grunnion: Etym: A Germanic name, formed from from oelf "elf" + riic "power".
Albus Dumbledore: Etym: From a root meaning "white". Cognate to Albion, a poetic term for Britain, usually translated as "White Isle".
Algie (PS ch. 7): Neville Longbottom's great-uncle who was forever trying to get Neville's magic to manifest itself.
Etym: Of Norman-French origin, meaning "with whiskers" or "mustaches".
Alicia Spinnet: Etym: Ultimately from Old German athal "noble" + haidu "kind, sort" (the equivalent to Modern English -hood).
Alohomora: Incantation for an unlocking charm.
Etym: Possibly Hawai`ian aloha "hello, goodbye", plus something I can't identify.
Ancient Runes: An elective subject at Hogwarts.
Ancient Runes Made Easy: A book Hermione was reading to prepare for taking Ancient Runes.
Angelina Johnson: Etym: "Little angel"; also a tree of tropical America, a genus of Leguminosae, with showy purple flowers.
Angus Fleet: Etym: As a name, probably from Old Irish AEngus "one choice". Also a breed of cattle, a 9th century saint, and a minor mythical hero.
Anti-Cheating Spell: Used on the quills the Hogwarts student use for their written exams. Probable mechanism: the pen senses when it's about to be used to write information obtained illicitly. Maybe if the student doesn't think they're cheating...
Aparecium: Incantation to be used with a Revealer.
Etym: The closest thing I can find is apertum, Latin for "open, uncovered, accessible".
Apparate: To perform an Apparation.
Apparation: The act of teleporting from one place to another.
Aragog: A giant, intelligent, spiderlike creature raised by Hagrid in his school days. Aragog now lives in the Forbidden Forest with his wife Mosag and their happy brood of scuttling flesh-eating spawn.
Etym: May be related to Gog and Magog, which among other things are the names of two giants in English legend, with ara- for "arachnid".
Argus Filch: Etym: A figure from Greek myth with a hundred eyes, killed by Hermes, after which his eyes were transferred to the tail of the peacock. By extension, a vigilant person.
Arithmancy: An elective subject at Hogwarts, taught by Professor Vector.
Armando Dippet: Etym: From Old German harja "host, army" + mana "man".
Arsenius Jigger: Etym: Arsenious means "of or relating to arsenic".
Arthur Weasley: Etym: From the name of the legendary king. Various Celtic derivations have been proposed, but most likely from a Roman gens named Artorius.
asphodel: In poetic use, the narcissus; ancient references are to the genus Asphodelus. An ingredient for the Draught of Living Death.
Azkaban: A prison for users of dark magic.
Etym: Origin unknown. Invented?