Etym: From the Gaelic name Dubhghall, from dubh "black" + gall "stranger".
Macmillan, Ernie: A Hufflepuff in Harry's year, now a prefect and a member of Dumbledore's Army.
Etym: Anglicized form of Mac Maoláin, from a diminutive form of maol, meaning "bald, tonsured" and in a transferred sense, a devotee of a saint.
Macnair, Walden: The former executioner for the Committee for the Disposal of Dangerous Creatures, now imprisoned in Azkaban for being a Death Eater.
Etym: HH has three possibilities, the most interesting being an anglicization of Mac an Mhaoir, "son of the steward, keeper". "The principal Irish family of this name held the hereditary post of Keeper of the Book of Armagh at Ballymoyer (Gaelic Baile an Mhaoir `town of the keeper')."
Madcap Magic for Wacky Warlocks: A book in the Hogwarts library.
Madley, Laura (GoF ch. 12): A Hufflepuff, 3 years behind Harry.
Etym: Name of several places in Britain, from the Old English words *mada (probably a derivative of maad, "foolish") + leeah "wood, clearing".
Mafalda Hopkirk: Etym: No etymology on this one, but it's the name of the socially concerned title character of a Portuguese comic strip.
Magical Drafts and Potions: A first-year textbook for Hogwarts students.
Magical Hieroglyphs and Logograms (OotP ch. 25): A book Hermione was reading to study for her O.W.L.s.
Magical Law Enforcement Patrol (OotP ch. 7): Alternate name for the Magical Law Enforcement Squad.
Magical Law Enforcement Squad: The ordinary police of the wizard world, as opposed to Aurors.
Magical Maintenance (OotP ch. 7): The department at the Ministry of Magic that decides what kind of illusory weather is visible out the windows. Uniform: navy robes.
Magical Me: Gilderoy Lockhart's most recent (and probably last) book of his exploits.
Magical Menagerie: The general pet store in Diagon Alley.
Magical Theory: A first-year textbook for Hogwarts students.
Magical Water Plants of the Mediterranean: A book lent to Neville by the fake Alastor Moody.
Magick Moste Evile (HBP ch. 18): A book in the Hogwarts library which does not detail Horcruxes.
Magnolia Crescent: A street near the Dursleys' home.
Magnolia Road (OotP ch. 1): Another street near the Dursleys' home.
Magorian (OotP ch. 30): A centaur living in the Forbidden Forest.
Etym: Couldn't find any.
mahogany: A tropical hardwood from several trees of the family Meliaceae, most often the West Indies mahogany, used mainly in furniture and paneling.
Maisie Cattermole: Etym: From a Gaelic form of Margaret (see Marge).
Malcolm Baddock: Etym: See below.
Malcolm (PS ch. 3): Part of Dudley Dursley's gang.
Etym: From Gaelic maol-Columb, "servant or disciple of Columb". Columb is the Gaelic form of the Latin Columba "dove", and was the name of a saint known as "the apostle of the Picts". Malcolm was also the name of several Scottish kings.
Malfoy, Abraxas (HBP ch. 9): Lucius Malfoy's father, known to Slughorn.
Etym: See below.
Malfoy, Draco: A Slytherin, the same year as Harry, who generously offered to introduce Harry to the "in" crowd and has not yet gotten over being snubbed. In Harry's second year and later, the Seeker for the Slytherin Quidditch team. In their fifth year, a prefect, for all the good it does him.
Etym: Stated by Rowling to be an invented name, from the French mal + foy or foi. Could be taken to mean "bad faith" as in a lack of faith or a false promise, or "faith in evil". We've certainly seen both out of the Malfoys by now.
In-depth article at HPLexicon
Malfoy, Lucius: A Death Eater of exalted lineage who has ascended the steps of societal power, taking hold of the scepter of leadership for the pure-blood faction, only to be smacked by the wet haddock of Voldemort's return and fall into the slimy canal of embarrassment at not being immediately thrilled at his former master's return. Now proving his everlasting loyalty by being locked up in Azkaban.
Etym: See above.
In-depth article at HPLexicon
Malfoy, Narcissa Black: Draco's mother.
Etym: See above.
Malfoy, Scorpius (DH ch. 37): Draco's son, off to Hogwarts with the rest of the lot.
Etym: See above.
Malkin, Madam (PS ch. 5): Proprietor of Robes for All Occasions in Diagon Alley.
Etym: As a surname, derived either from the medieval female given name Malle, or the Yiddish name Malke, from the Hebrew word malka "queen". OED also gives it as a name for a woman of the lower classes in various proverbial expressions; the name of a female spectre or demon; dialectual name for a cat; or an effeminate man. If I had to guess, I'd go with the female spectre.
mallowsweet (OotP ch. 27): Something in the family Malvaceae which centaurs burn along with sage for divinatory purposes.
mandrake: In these books, a plant which resembles a humanoid with a normal-looking plant growing out of its head. The scream of a mature mandrake can kill, while that of a young one will still stun a person. Mandrakes can be used to restore a person who has been paralyzed by a basilisk.
The real mandrake is any of the six species of the genus Mandragora, alleged to have all sorts of magical powers, and said to produce the scream when pulled from the ground.
Mandrake Restorative Draught: The potion made from mandrakes which can cure a person who has been paralyzed by a basilisk.
Mandy Brockelhurst [Amanda]:
Etym: Latin for "fit to be loved", also translated as "beloved".
manticore: A mythological creature with the body of a lion, the head of a man, sharp quills like a porcupine, and the tail of a scorpion.
maple: Any tree of the genus Acer, comprising the sugar maple, several varieties that provide a dense, hard wood used in furniture, and many ornamental trees.
Marauders, the: What James Potter, Sirius Black, Remus Lupin, and Peter Pettigrew called themselves at school.
Marauder's Map: A magical map created by Messrs. Moony, Wormtail, Padfoot, and Prongs, which shows all of Hogwarts, the locations of all people therein, and instructions for opening the various secret passages out of the school.
Marchbanks, Griselda (OotP ch. 31): The head of the Wizarding Examinations Authority, and an elder of the Wizengamot until resigning in protest at the introduction of the High Inquisitor.
Etym: A Scottish surname, said to date from the 16th century when a family previously named Johnston acquired an estate by the name of Ratho-Majoribankis.
Marcus Belby: Etym: See below.
Marcus Flint: Etym: Probably derived from Mars. If this name is meant as a historical reference, then it's got to be Marcus Antonius aka Mark Antony.
Marge (Marjorie) Dursley (PS ch. 2):
Etym: From a French form of Margaret, derived from the Greek for "pearl". St. Margaret is the patron saint of Scotland.
Marietta Edgecombe: Etym: Modern use of this name appears to originate with a town in Ohio named for Marie Antoinette.
Marius (DH ch. 26): A Ministry wizard helping guard Gringotts.
Etym: Possibly named for Gaius Marius, a Roman general turned consul turned insane execution-happy old guy.
Mark Evans: Etym: The modern form of Marcus, the name of 2 saints.
Marlene McKinnon: Etym: This name was invented for Marlene Dietrich by telescoping her original first and middle names of Maria Magdalena.
Mars: Stemming from its association with the Roman god of war, Mars is often associated with conflict and death in astrology.
Marsh, Madam (PoA ch. 3): A frequent passenger on the Knight Bus.
Etym: Derived from the Old English word for same.
Martha (HBP ch. 12): An assistant at the orphanage that raised Tom Riddle.
Etym: From Aramaic mar "lord". The name is used as a Biblical allusion to concern with domestic affairs.
Mary Elizabeth Cattermole: Etym: See Molly.
Mary Dorkins: Etym: See Molly.
Marvolo Gaunt: Etym: See below.
Marvolo Riddle, Tom: Etym: Probably invented to make the anagram come out right.
Masons (CoS ch. 1): A builder (contractor) and his wife that the Dursleys had over for dinner in an attempt to get a large drill order out of them.
Etym: What it looks like; the surname derives from being an occupational name for a stonemason.
Maxime, Olympe: The headmistress of Beauxbatons, alleged by Hagrid to be a half-giant but not admitting to it yet.
Etym: Probably invented as a cognate to "maximum".
McDonald, Natalie: A Gryffindor, 3 years behind Harry.
Etym: From a Gaelic patronymic deriving from dubno "world" + val "might, "rule".
McGonagall, Minerva: Head of Gryffindor House, and the Transfiguration instructor.
Etym: Patronymic from the name Congal, composed of the Old Celtic words for "high" and "valor", appropriate for a Gryffindor. However, the professor is actually named for a Scottish poet reputed to be the worst ever to, er, grace the English language.
In-depth article at HPLexicon
McGuffin, Jim (PS ch. 6): A TV weatherman.
Etym: Name etymology is probably not relevant. The name was used as a term by Alfred Hitchcock to mean an object that is significant to a plot. Okay, that's probably not relevant here either.
McKinnon, Marlene (OotP ch. 9): An early member of the Order of the Phoenix who was killed by Voldemort along with her husband.
Etym: Anglicized form of Mac Fhionghuin, from the name meaning "fair born" or "beloved son".
McLaggen, Cormac (HBP ch. 7): A student one year ahead of Harry, a member of the Slug Club, and briefly the Gryffindor Keeper.
Etym: Couldn't find anything.
Meadowes, Dorcas (OotP ch. 9): A member of the Order of the Phoenix who was killed by Voldemort during his earlier reign.
Etym: Originally a name for someone living by a meadow.
Medal for Magical Merit: Tom Riddle was awarded one during his days at Hogwarts.
Medieval Assembly of European Wizards: Something the History of Magic class was assigned to write a yard-long essay about.
mediwizard: A wizard paramedic.
Meliflua, Araminta (OotP ch. 6): A cousin of Madam Black's who tried to make Muggle-hunting legal.
Etym: If she was making legislation, she was probably a mellifluous speaker.
Melinda Bobbin: Etym: A name of recent invention, from adding -inda to Melissa or Melanie.
Memory Charm: A spell that causes the target to forget about something. Incantation: Obliviate.
Men Who Love Dragons Too Much: A book in the Hogwarts library.
Merlin (PS ch. 6): The best-known wizard in English folklore, and also apparently in the British wizard community, as evidenced by the Order of Merlin.
Mermish: The language of merpeople.
Merope Gaunt (Riddle):
Etym: One of the Pleiades, the only one to fall in love with a mortal. Also, meropia is a dullness or obscuration of sight.
merpeople: Mermaids and mermen, not on the best terms with air-breathers. A town of them is located at the bottom of the lake by Hogwarts.
Merrythought, Galatea (HBP ch. 17): The last person to remain as Defense Against the Dark Arts teacher for more than a year.
Etym: I think the meaning is literal; incidentally, this is also apparently a term for a wishbone.
Metamorphmagus (OotP ch. 3): A witch or wizard with the inborn ability to change their appearance at will. Not their overall shape, though, as far as we can tell.
Metamorph-Medal (HBP ch. 5): A sham amulet sold with the promise to allow the wearer to alter their appearance like a Metamorphmagus.
Michael Corner: Etym: The name of the head Biblical archangel, from Hebrew for "Who is like the Lord?"
Midgen, Eloise (GoF ch. 13): A girl who tried to curse her acne off and ended up removing her nose (reattached, though slightly off-center).
Etym: No info found.
Miles Bletchley: Etym: From Old German Milo, possibly related to Old Slavonic milu "merciful" (not in this case, though).
Millamant's Magic Marquees (DH ch. 6): A magical pavilion-maker.
Etym: The name of a character in William Congreve's play The Way of the World.
Millicent Bagnold: Etym: See below.
Millicent Bulstrode: Etym: From the Old German name Amalasuintha, composed of amal "work" + swintha "strong".
Mimbulus mimbletonia (OotP ch. 10): The Latin name for the plant that produces stinksap.
Etym: Variation on the real genus Mimulus, used as a folk remedy for shyness, anxiety, and forgetfulness.
Mimsy-Porpington, Sir Nicholas de: Aka Nearly Headless Nick, the house ghost of Gryffindor. He celebrated his 500th deathday on Halloween, 1992. If this count includes the shift to the Gregorian calendar, it means he died on October 20th or 21st, 1492.
Etym: Mimsy was a word invented by Lewis Carroll for his poem "Jabberwocky", and has been defined as "prim, prudish, contemptible". No idea about Porpington.
Minerva McGonagall: Etym: Probably of Etruscan origin, this is the Roman equivalent to Athena, the goddess of wisdom and valor.
Minister of Magic: The head of the Ministry of Magic.
Ministry of Magic: A secret Cabinet-level department of the UK government, charged with providing civil services to wizard-dom. The current Minister of Magic is Cornelius Fudge.
The Ministry is divided into these departments, which contain further subentities (see the department entries for lists):
Department for the Regulation and Control of Magical Creatures
Department of International Magical Cooperation
Department of Magical Accidents and Catastrophes
Department of Magical Games and Sports
Department of Magical Law Enforcement
Department of Magical Transportation
Department of Mysteries
We don't know which departments these belong to:
Committee for the Disposal of Dangerous Creatures (probably the
Department for the Regulation and Control of Magical Creatures)
Committee on Experimental Charms
Misuse of Muggle Artifacts Office
Minsk (OotP ch. 20): A place in eastern Russia where Hagrid had an argument with a vampire.
Miranda Goshawk: Etym: Invented by Shakespeare, from Latin for "worthy to be admired".
Miriam Strout: Etym: Probably, like Mary, from the Hebrew for "wished-for child", though the alternative merî, "rebellion" has been posited.
Mirror of Erised: A magical device which entraps its viewer by showing them impossible scenes of what thay most desire, entrapping the viewer to stare blankly at it for hours. Muggles have managed to build a crude version of this.
Misuse of Muggle Artifacts Office: The department of the Ministry of Magic which enforces laws on enchanting certain proscribed objects and tries to keep enchanted objects of all sorts away from Muggles.
Moaning Myrtle: The ghost of a Hogwarts student who haunts a stall in the first-floor girls' bathroom. She was killed by Tom Riddle when he first opened the Chamber of Secrets.
Etym: Myrtle refers to various shrubs of the genus Myrtus.
Mobiliarbus: An incantation to levitate a tree.
Etym: Probably supposed to be Latin, "moving tree". "Tree" is in fact arbor.
Mobilicorpus: An incantation to levitate a body.
Etym: Latin, "moving body".
Mockridge, Cuthbert (GoF ch. 7): The head of the Goblin Liaison Office.
Etym: From the town of Mogridge in Devon, whose name comes from Old English Mogga, probably a personal name, and hrycg "ridge, spur".
Modern Magical History: A book in the Hogwarts library.
mokeskin (DH ch. 7): A pouch made of it will allow no one but the owner to remove an object from it. Mokes are very rare (even rarer now that Hagrid got hold of one to make the pouch).
Molly Prewett Weasley: Etym: A form of Mary, from a Hebrew name probably meaning "wished-for child".
Molly Weasley Potter, Ginny: Etym: See above.
Mollywobbles (HBP ch. 86): Arthur Weasley's nickname for Molly. Note for students of stealth: a secret password is not a secret password if you're going to say it in front of the kids.
monkshood: see wolfsbane.
Monica Wilkins: Etym: Unknown; name of the mother of St. Augustine.
Monster Book of Monsters, The: The textbook for the Care of Magical Creatures class.
Montague (PoA ch. 15): A Chaser on the Slytherin Quidditch team, he became team captain in Harry's fifth year, though he may not be anymore if he never recovers from his experience with the Vanishing Cabinet.
Etym: From a place name in La Manche, from Old French mont "hill" + agu "pointed", or an Anglicized form of Mac Taidhg, from a name meaning "poet, philosopher". Also the family name of the late-medieval Earls of Salisbury.
Montgomery (HBP ch. 22): The last name of two sisters at Hogwarts whose brother was killed by a werewolf (probably Fenrir Greyback).
Etym: From Old French mon "hill" plus a Germanic name composed of guma "man" + riic "power".
Moody, Alastor: An Auror, instrumental in rounding up the Death Eaters after Voldemort's fall, appointed to teach Defense Against the Dark Arts in Harry's fourth year, but captured and impersonated by Bartemius Crouch. Nicknamed "Mad-Eye" for the magical device which takes the place of his natural left eye, but even with that, killed when he failed to exercise constant vigilance at a crucial moment.
Etym: HH: "Nickname for a courageous, arrogant, or foolhardy person, or one quickly moved to anger." Or we could just be supposed to look at the modern English word.
Moon (PS ch. 7): A student in the same year as Harry, house unknown.
Etym: Several possibilities: the French town Moyon; Anglo-Norman French moun "monk"; Cornish mon "thin"; or a diminutive of the Gaelic word for "early, timely".
moonstone (OotP ch. 12): Has various meanings, but to the ancients it was selenite, which was believed to help with prediction of the future and to reconcile lovers.
Moony: Remus Lupin's nickname during his school days.
Mopsus: A discarded character, mentioned by Rowling in this interview, who would have been a True Seer present in the first book.
Etym: The name of not one but two seers in Greek myth.
Morag MacDougal: Etym: Gaelic, a diminutive of mor(a), meaning "the sun".
Moran (GoF ch. 8): A Chaser on the Irish national Quidditch team.
Etym: Gaelic mórán "great, large".
Morfin Gaunt: Etym: Might be a distant relative of Mervin, which is from mer, which may mean "marrow" and myn "eminent". ECN mentions that this was the name of "a shadowy Welsh king" of the 9th century.
Morgana (PS ch. 6): A sorceress who, in some versions of the Arthurian legend, was Arthur's sister and helped bring about his downfall. Featured in the Famous Witches and Wizards trading card series.
Morsmordre: The incantation that conjures the Dark Mark.
Etym: "Death mark", from Latin mors "death" and French mordre "to bite, cut".
Mortlake (CoS ch. 14): A wizard raided by the Misuse of Muggle Artifacts Office who turned out to be law-abiding except for the presence of "some extremely odd ferrets".
Mosag (CoS ch. 16): Aragog's wife, procured for him by Hagrid.
Etym: No etymology.
Mostafa, Hassan (GoF ch. 8): The chair of the International Association of Quidditch, and referee for the Quidditch World Cup.
Etym: Variation of Mustafa, meaning "chosen, selected, preferred".
Most Charming Smile Award: Awarded by Witch Weekly five times to Gilderoy Lockhart.
Moste Potente Potions: A book in the Restricted Section of the Hogwarts library; contains the formula for the Polyjuice Potion.
Most Extraordinary Society of Potioneers (HBP ch. 9): A group founded by Hector Dagworth-Granger.
Mould-on-the-Wold (DH ch. 11): The village the Dumbledore family originally lived in.
mountain troll: The variety of troll that got loose in Hogwarts on Halloween; apparently one of the lesser varieties.
Mr. Paws (PS ch. 3): One of Mrs. Figg's cats.
Mrs. Skower's All-Purpose Magical Mess Remover: Pretty much what it claims to be.
Etym: Skower is an invented variation on scour.
Mudblood: Extreme pejorative for someone with any non-magical ancestry. Users of this word contrast themselves as pure-bloods.
Muffliato (HBP ch. 12): A spell to keep nearby peopl from eavesdropping.
Etym: Derived from muffle.
Muggle: 1) A person who is not part of, or was not raised in, the wizard society. 2) A person with no magical powers.
Etym: Stated by Rowling to be invented from the British slang meaning of mug, "a dupe". Coincidentally an actual archaic English word, as has been discussed at length elsewhere.
Muggle-born Register (DH ch. 11): A survey by the Ministry of Magic to better understand magical genetics.
Muggle-born Registration Commission (DH ch. 11): The committee compiling the Muggle-born Register.
Muggle Protection Act: A proposed new law (possibly passed by now).
Muggle Repelling Charms: Spells that keep prying non-magical people away from large gatherings of wizards (such as the Quidditch World Cup).
Muggle Studies: An optional class at Hogwarts.
Muggle-Worthy Excuse Committee (OotP ch. 7): A division of the Ministry of Magic, which may be for coming up with explanations of bizarre things that Muggles inadvertently see.
Mugwump: Albus Dumbledore is a (or the) supreme one.
Etym: Not sure of the meaning in this context, but it was 18th/19th century slang for a person disinterested in party politics, an independent thinker, or, alternatively, a major "boss". The term originates from a Natick Indian word for a major chief.
Mulciber (GoF ch. 30): A Death Eater, imprisoned in Azakaban until recently, briefly sprung and then sent right back after the battle at the Ministry of Magic.
Etym: Another name for Vulcan/Hephaestus, the god of the forge and weaponsmith to Zeus, whose smithy was said to be in Mount Etna.
Mullet (GoF ch. 8): A Chaser on the Irish national Quidditch team.
Etym: From Middle English mule, meaning, you guessed it, "mule".
Mundungus Fletcher: Etym: Offal, refuse, or bad-smelling tobacco, from Spanish mondongo, meaning "black pudding" or "tripe"... like that thing about his 12-person tent.
Murcus (GoF ch. 26): The chieftainess of the merpeople who live by Hogwarts.
Etym: OED has an entry for murcous, meaning having had a thumb cut off, from a Latin word meaning "one who cuts his thumb off to avoid military service". Er, no, I don't think so either.
Muriel (HBP ch. 29): A great-aunt of Molly Weasley.
Etym: Of uncertain origin, possibly from Irish muir "sea" + geal "bright".
murtlap (OotP ch. 15): Some magical creature that has tentacles, the essense of which aids in healing.
Etym: No idea.