Etym: The Middle English spelling of abbot, just the thing to go along with the Fat Friar.
Abercrombie, Euan (OotP ch. 11): A Gryffindor, 4 years behind Harry.
Etym: Last name of a British general who participated in the French and Indian Wars.
Aberforth Dumbledore: Etym: No name-specific info. Aber in Scottish placenames means "confluence" or "river mouth", so it could mean the location of Edinburgh-- at the mouth of the river Forth.
Abergavenny: A town in Wales where the Knight Bus dropped off a Madam Marsh.
Abraxan horse (OotP ch. 20): A variety of winged horses.
Etym: Looks like it's from Abraxas, a word used in magical amulets and later turned into a Gnostic deity, though what that implies I have no idea.
Acanthia Way (OotP ch. 10): The address given in Little Norton for Doris Purkiss.
Etym: Various plants in the genus Acanthus; the leaf of A. spinosa became a popular classical decorative motif.
Accidental Magic Reversal Squad: An arm of the Ministry of Magic which rescues and restores the victims of splinching and other magical accidents.
Accio: The incantation for a Summoning Charm, usually followed by the name of the item summoned.
Etym: Latin, "I summon".
Achievement in Charming (OotP ch. 31): A book Hermione was studying for her O.W.L.s from.
Ackerley, Stewart [Acker] (GoF ch. 12): A Ravenclaw, three years behind Harry.
Etym: From a Middle English or German word for "field".
Acid Pops: A magical candy capable of actually burning a hole through one's tongue.
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.
Agatha Timms: Etym: From Greek agathos, "good". St. Agatha is a martyr of possibly the 3rd century.
Age Line: A barrier which stops anyone below a certain age crossing it.
Aging Potion: Can age a person physically, but does not fool an Age Line.
Agnes (OotP ch. 23): A witch confined to the Janus Thickey Ward.
Etym: From Latin agnus, "sheep". In this case, a sheep in wolf's clothing.
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.
Aidan Lynch: Etym: Diminutive of Old Irish aid "fire".
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.
Alastor Moody: Etym: PN: "In Greek legend an avenging deity who drives the sinner to fresh crimes. Shelley's Alastor is, however, the Spirit of Solitude." Having seen what Moody thinks of Snape, that first part sounds rather ominous... Also used to name the target that the deity takes over, rather like Moody's form being used for evil purposes.
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".
Ali Bashir: Etym: Anglicization of an Arabic name derived from from `ala, "rise, ascend".
Alice Longbottom: Etym: From Old German athal "noble" + haidu "kind, sort"
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.
Alphard (Black?): Etym: A star whose common name means "the solitary one".
Amelia Susan Bones: Etym: ECN says it's derived from the Old German name element amal- "work", but OED claims it's from Latin melior "better". The intended etymology is probably the latter.
Amos Diggory: Etym: From Hebrew for "carried", an Old Testament prophet with a message of doom.
Ancient Runes: An elective subject at Hogwarts, which Hermione is taking.
Ancient Runes Made Easy: A book Hermione was reading to prepare for taking Ancient Runes.
Andrew Kirke: Etym: From the Greek for "manly"; also the name of the patron saint of Scotland and Russia. The saint's name is probably derived from a Hebrew name.
Andromeda Black Tonks: Etym: A mythical woman who was to be sacrificed to a sea monster because of her mother's boasting, saved by Perseus who killed the sea monster and an uncle who intended to marry her. In keeping with the astronomical names of the Black family, also the closest galaxy to our own.
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.
Animagus: A wizard who can transform at will (along with their clothes and anything they may be carrying) into a characteristic animal form. The Ministry of Magic maintains a registry of Animagi, but unregistered ones abound. Animagi revealed so far are James Potter, Peter Pettigrew, Sirius Black, Rita Skeeter and, the only registered one mentioned here, Professor McGonagall.
Etym: I'm guessing this is not "animal mage" but "spirit mage", from Latin anima.
Anthology of Eighteenth-Century Charms, An: A book in the Hogwarts library.
Anthony Goldstein: Etym: Unknown. The name of a couple saints.
Anti-Cheating Charms (OotP ch. 31): Probably the same as the Anti-Cheating Spell, used on the O.W.L. exam papers.
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...
Anti-Disapparation Jinx (OotP ch. 36): A spell that disables the target's ability to Apparate.
Antonin Dolohov: Etym: Cognate of Anthony, whose etymology is unknown. St. Anthony is the patron saint of swineherds.
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 Test Center (OotP ch. 7): The arm of the Ministry of Magic that certifies people to allow them to perform Apparation.
Apparation: The act of teleporting from one place to another. The Ministry of Magic requires those who want to use it to pass a test and get a license, as it can be dangerous. The grounds of Hogwarts are enchanted to make Apparation impossible there.
Appraisal of Magical Education in Europe, An: A book which contains information on Durmstrang and Beauxbatons.
Apollyon Pringle: Etym: A name for the Devil, meaning "destroyer". And we thought Filch was bad...
Aquavirius maggots (OotP ch. 34): Whatever they are, The Quibbler thinks the Ministry of Magic is breeding them.
Etym: Think it's from the Latin roots for "water" and "life".
Arabella Doreen Figg: Etym: A name of Scottish origin and unknown etymology, possibly from Latin Orabilis "easy to be entreated"; also the title character of a Strauss opera.
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".
Araminta Meliflua: Etym: Started as an invented name, possibly conflated from Arabella and Aminta.
Archie [Archibald] (GoF ch. 7): A wizard in attendance at the Quidditch World Cup who is not entirely in tune with Muggle fashions.
Etym: From Old German ercan "genuine, simple" + bald "bold".
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.
Argyllshire: A hilly and remote section of Scotland. The Fat Lady hid in a map of it after being attacked by Sirius Black.
Arithmancy: An elective subject at Hogwarts which Hermione is now taking, taught by Professor Vector.
armadillo bile: Apparently, a basic potionmaking supply used by Hogwarts students.
Armando Dippet: Etym: From Old German harja "host, army" + mana "man".
Arnold Peasegood: Etym: From Old German arin "eagle" + vald "power".
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.
ash: Any tree of the genus Fraximus. Wood of the commercial varieties is stiff, strong, resilient, and lightweight, and frequently used in tool handles and sports equipment.
asphodel: In poetic use, the narcissus; ancient references are to the genus Asphodelus. An ingredient for the Draught of Living Death.
Asiatic Anti-Venoms (OotP ch. 16): A book in the Hogwarts library.
Augustus Pye: Etym: See below.
Augustus Rookwood: Etym: Latin, meaning "venerable, consecrated".
Aurors: Wizards employed by the Ministry of Magic to hunt down users of dark magic. Frank Longbottom and Alastor Moody are ex-Aurors.
Etym: British slang calls policemen coppers. Auror could easily be from aureum, Latin for "gold".
Auror Headquarters (OotP ch. 7): Located in the Ministry of Magic.
Auto-Answer Quills (OotP ch. 31): A banned item at O.W.L. exams.
Avada Kedavra: Incantation for the Killing Curse.
Etym: Several Web sites (including an earlier version of this one, mea culpa) have given this as the root of abracadabra, originating as a Kabalistic term. Instead, it appears that abracadabra comes from Abraxas via Gnostic occultism, and I haven't been able to find anything on the origins of avada kedavra.
Avery: A Death Eater, left at large after claiming he had been a victim of the Imperius Curse, but imprisoned after the battle at the Ministry of Magic.
Etym: A variation of the Germanic name Alberic, from oelf "elf" + ric "power". John Avery was a renowned pirate of the late 17th century.
Avis: Incantation to conjure birds from one's wand.
Etym: Latin, "bird". Technically, should be the plural, aves.
Axminster: A type of flying carpet used in Britain before carpets were added to the Registry of Proscribed Charmable Objects.
Etym: An Axminster carpet refers to a type originally made by a factory in Axminster, Devon, from 1755 to 1835.
Azkaban: A prison for users of dark magic, staffed by dementors.
Etym: Origin unknown. Invented?