Leaky Cauldron, The: A wizards' pub located somewhere in London; the primary entrance to Diagon Alley.
Lee Jordan: Etym: The sheltered side of something, or dregs. As a name, from Old English leeah "meadow".
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.
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".