Lampadomancy - a lamp flame was the tool for this type of Divination.

Langlock (Spell) - the Half-Blood Prince's jinx which glues one's tongue to the roof of one's mouth.

Latin - see Magic Words - the language of ancient Rome, that gave rise to the "romance" languages: Italian, French, Spanish and Portuguese. Once the Romans conquered Europe about two thousand years ago, Latin became the common language. Scholars in particular used it, writing most books in Latin, and it became the primary language of Christianity.

Wizards also rely on Latin for many spells, curses and charms. And the motto for Hogwarts is Latin: Draco dormiens nunquam titillandus ("Never tickle a sleeping dragon").

Leaping Toadstool (Plant) - an example of magical fauna studied in second year Herbology.

Legilimency - the ability to draw emotions and memories from the mind of another.

Leprechaun (sometimes called Clauricorn) - tiny, mischievous creatures that resemble little green humans. They are the mascots of the Irish National Quidditch Team. While they guard ancient buried stores of gold and other valuable treasure, they also make a gold-like substance that vanishes after an hour or two -- Leprechauns' gold.

Lethifold - a very dangerous creature, thankfully rare, found only in the tropics. It looks like a black cloak at least half an inch thick (thicker if it has recently hunted and digested). It glides along the ground at night, and usually enfolds the sleeping and suffocates its victim, then digests them completely. The only spell which repels a lethifold is the Patronus Charm.

Levicorpus (Spell) - the Half-Blood Prince's spell which up ends someone in the air as if they're suspended by an ankle.

Liberacorpus (Spell) - Counterjinx to Levicorpus and created by the Half-Blood Prince.

Libranomancy (Divination) - the study of incense smoke and the patterns it makes.

Lithomancy (Divination) - gemstones could predict the future

Lobalug - a creature living at the bottom of the North Sea, it is ten inches long and consists only of a rubbery spout and venom sac.

Locomotor Mortis (Spell) - the leg-locking curse.

Lovage (Plant) - an ingredient in Confusing and Befuddlement Draughts.

Lumos (Spell) - a spell used to create light.

Lumos Solarum (Spell) - this spell creates a blast of light as bright as the sun.