Etym: Laburnum is a genus of ornamental but poisonous trees and shrubs.
lacewing flies: An ingredient for the Polyjuice Potion. This could refer to anything in the order Neuroptera, particularly in the family Chrysopidae (green lacewings) or Hemerobiidae (brown lacewings).
Lachlan the Lanky (OotP ch. 13): A historical figure of whom there is a statue in Hogwarts.
Etym: Possibly from Gaelic laochail "warlike".
Ladislaw Zamojski: Etym: Name shared, with various other spellings, by kings of Bohemia, Hungary, and Naples. No info on what it actually means.
Lavender Brown: Etym: Lavandula vera, used for perfumes. The flower signifies distrust.
Leaky Cauldron, The: A wizards' pub located somewhere in London, along Charing Cross Road; the primary entrance to Diagon Alley.
Leaving Feast: The traditional end-of-school-year feast, held the night before everyone goes home on the Hogwarts Express.
Lee Jordan: Etym: The sheltered side of something, or dregs. As a name, from Old English leeah "meadow".
leeches: An ingredient for the Polyjuice Potion. The type of leech needed for magic is probably the European medicinal leech, Hirudo medicinalis.
Legilimency (OotP ch. 24): The magical art of rooting around in someone else's mind. Incantation: Legilimens.
Legilimens (OotP ch. 24): The incantation for Legilimency; also someone who practices it.
Etym: Latin, legere "read" + mens "mind, intellect".
Leg-Locker Curse: A spell that paralyzes the legs. Incantation: Locomotor Mortis.
Lestrange, Bellatrix Black: A Death Eater cousin of Sirius's, doing her darndest to make up for how little help he's given the dark side of wizardry.
Etym: Derived from strange as you might expect. A Sir Roger L'Estrange, an early English journalist and pamphleteer, was a Royalist supporter during the English Civil Wars and Commonwealth period, and was imprisoned for four years after being implicated in an unsuccessful attempt to capture the town of Lynn, Norfolk for the Royalists.
Lestrange, Rabastan (OotP ch. 6): Rodolphus's brother, also a Death Eater, sprung from Azkaban briefly but recaptured at the Ministry of Magic.
Etym: See above.
Lestrange, Rodolphus (OotP ch. 6): Bellatrix's husband, also a Death Eater, also imprisoned in Azkaban, but, unlike her, recaptured at the Ministry of Magic.
Etym: See above.
Levski: A Chaser on the Bulgarian national Quidditch team.
Etym: No etymology found, but this was the byname of Vasil Ivanov Kunchev (1837-1873), a Bulgarian revolutionary leader.
Licorice Wands: A wizard candy, undoubtedly very tasty if you happen to like licorice.
Lily Evans Potter: Etym: As a personal name, probably derives from a pet form of Elizabeth. In the plant world, anything in the genus Lilium. Different types of lily have different meanings; if a specific one is intended, it's probably "purity and sweetness", the white lily. Outside possibilities are "majesty", for the imperial lily, or "return of happiness", the lily of the valley.
lionfish: Several species of fish of the family Scorpaenidae. The spines, which contain a mild venom, are a basic potion-making supply.
Lisa Turpin: Etym: Another nickname from Elizabeth, which is from Hebrew Elisheba, "my God (is) satisfaction".
Little Hangleton: The location of the Riddle House and The Hanged Man, 200 miles from Little Whinging. Apparently fictional, though there is a just plain Hangleton in Sussex.
Little Norton (OotP ch. 10): The home of Doris Purkiss.
Little Whinging: The town in Surrey in which the Dursleys live. Does not appear to be a real town.
Lockhart, Gilderoy: A best-selling author, honorary member of the Dark Force Defense League, five-time winner of the Witch Weekly Most Charming Smile Award, and the Defense Against the Dark Arts teacher in Harry's second year. Owing to a bungled Memory Charm, he is now confined to St. Mungo's Hospital, and unlikely to write anything more unless it's Psessions with Psychologists.
Favorite color: lilac. Ideal birthday gift: harmony between magic and non-magic peoples. Secret ambition: Rid the world of evil and market his own line of hair-care products.
Etym: EB has an entry for John Gibson Lockhart (1794-1854) a Scottish writer, best remembered for his Life of Sir Walter Scott, "one of the great biographies in English". Appropriate for a thief of biographies.
Locomotor (OotP ch. 3): Generalized incantation to give an object the power of independent movement.
Etym: Latin for "that which has locomotive power".
Locomotor Mortis: Incantation for the Leg-Locker Curse.
Etym: Latin, "appendage" and "death".
Longbottom, Alice: Neville's mother, tortured by the Death Eaters to try and get information out of Neville's father. Confined to St. Mungo's Hospital along with her husband.
Etym: See below.
Longbottom, Frank (GoF ch. 30): Neville's father, an Auror who was captured and tortured by the Death Eaters after Voldemort's fall. Now confined to St. Mungo's Hospital.
Etym: See below.
Longbottom, Neville: A Gryffindor, same year as Harry, with the worst memory in his class. Nevertheless, now a member of Dumbledore's Army.
Etym: Place name from western Yorkshire, from Middle English for "long valley".
lovage (OotP ch. 18): Levisticum officinale, used in our world as an herbal tea, a seasoning, and a perfume oil. In the magical world, a common ingredient of Confusing Draughts and Befuddlement Draughts.
Lovegoods: Acquaintances of the Weasley family who arrived at the Quidditch World Cup site a week before them. Mr. Lovegood runs The Quibbler.
Etym: No etymology.
Lovegood, Luna (OotP ch. 10): A Ravenclaw a year behind Harry, and a member of Dumbledore's Army.
Etym: None found.
Lucius Malfoy: Etym: From Latin lux, light; possibly intended as a reference to Lucifer, "light-bearer". The name of three popes, including the patron saint of Copenhagen, who succeeded St. Cornelius and continued his policies... does this mean we'll be seeing a new Minister of Magic? EB also gives this as an obsolete form of luscious, but let's not go there.
Ludicrous Patents Office (OotP ch. 7): A function of the Ministry of Magic.
Ludo (Ludovic) Bagman:
Etym: Ludo is a game similar to pachisi/parcheesi. The word is Latin for "I play".
Lumos: An incantation to make one's wand glow.
Etym: Pseudo-Latin/Greek for "light".
Luna Lovegood: Etym: The Latin name for the moon, which does have a linguistic connection with lunatic.
Lupin, Remus J.: The Defense Against the Dark Arts teacher in Harry's third year. Removed after he was revealed to be a werewolf, due to some parents having small-minded knee-jerk prejudices against allowing their children into close proximity with someone who can turn into a man-eating monster. Lupin was also one of James Potter's close friends during their school days.
Etym: A variation on lupine.
Lynch, Aidan (GoF ch. 8): The Seeker on the Irish national Quidditch team.
Etym: Anglicized form of Ó Loingsigh, from a given name meaning "mariner", or of Linseach, a name of unknown origin.