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.
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.
Leg-Locker Curse: A spell that paralyzes the legs. Incantation: Locomotor Mortis.
Licorice Wands: A wizard candy, undoubtedly very tasty if you happen to like licorice.
Lily 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.
Lisa Turpin: Etym: Another nickname from Elizabeth, which is from Hebrew Elisheba, "my God (is) satisfaction".
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 Mortis: Incantation for the Leg-Locker Curse.
Etym: Latin, "appendage" and "death".
Longbottom, Neville: A Gryffindor, same year as Harry, with the worst memory in his class.
Etym: Place name from western Yorkshire, from Middle English for "long valley".
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.
Lumos: An incantation to make one's wand glow.
Etym: Pseudo-Latin/Greek for "light".
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.