A-G:
Accio
Latin for “to summon�? Summoning charm, used to make objects fly straight to the spell caster.
Aguamenti
Causes a jet of water to come from the end of the caster's wand. The speed of the jet is controllable: Harry used it to refill a small goblet in the Horcrux cave, whilst a short while later, he and Hagrid used it to douse the flames on Hagrid's Hut when it was on fire.
Alohomora
From Hawaiian “Aloha�?which means “hello/farewell�?and Latin “mora�?which means “obstacle�? This spell is used to open a locked door or window. While it will not unlock all magically sealed doors, it works well against "Colloportus."
Anapneo
Greek for "breathe". Clears the airways of the person who the spell is cast upon, allowing them to breathe properly. Horace Slughorn cast this on Marcus Belby when he accidentally swallowed a large mouthful of pheasant.
Anti-Cheating Spell
A spell that teachers at Hogwarts use on quills or exams to prevent cheating.
Anti-Disapparation Jinx
When cast on a person, it prevents them from Disapparating. Dumbledore used this jinx to bind the Death Eaters in the Death Chamber at the Ministry of Magic.
Anti-Intruder Jinx
Repels intruders. These were cast on the Hogwarts walls for the 1996-97 school year to protect the students following the return of Voldemort.
Aparecium
“Appareo�?is Latin for “appear�?or "to become visible". Used to reveal invisible ink.
Apparate
“Appareo�?is Latin for “to become visible�? This spell allows the spell caster to appear instantly in a given place. It is used in conjunction with Disapparate. The caster must Disapparate from one location in order to Apparate in another.
Avada Kedavra
A corruption of "abracadabra" which was used as a Healing Spell to drive disease from the patient's body in the Middle Ages. Its likely source is either the Arabic "abra kadabra" (may the things be destroyed), or the Aramaic "abhadda kedhabhra" (disappear with these words).
The Killing Curse. It requires a strong bit of magic behind it; the incantation alone is not enough for the spell to work. When cast effectively, Avada Kedavra kills instantaneously, producing a blinding flash of green light but leaving no mark on the victim's body. There is no way to block or counter the Killing Curse, and the only people ever to survive it are Harry Potter and Tom Riddle. Avada Kedavra is one of the three Unforgivable Curses and its use against another human being is punishable by a life sentence in Azkaban.
Avis
Latin for “bird�? Conjures a flock of birds.
Backfiring Jinx
Effect unknown, but the casting of such a jinx in Elephant and Castle (a district of London) was serious enough to require the Magical Law Enforcement Squad to be called out.
Babbling Curse
Causes the victim to babble nonsense. Lockhart once cured someone of this curse on his travels. Or not.
Banishing Charm
The opposite of Accio, causes an object to fly away from the caster.
Bat-Bogey Hex
Maybe the effects of this are best left to the imagination. Causes bogies to grow, become bat-like, and attack the victim. Ginny casts this spell on Draco Malfoy in Order of the Phoenix.
Bubblehead Charm
Used to create a bubble of air around the caster’s head. Often used to allow the caster to breathe underwater.
Cheering Charm
Not much is known about these, but it’s safe to assume that they make people happy.
Colloportus
From the Latin "colligere," meaning "bind together" and "portus," meaning door. This spell is used to magically seal doors, but is not particularly effective. It can easy be countered with Alohomora, which will open any door sealed with Colloportus.
Colour-Change Charm
Causes an object to change colour. This spell also works on organic matter, as Harry was meant to cast it on a rat during his Charms OWL in order to turn it orange. Unfortunately he got the incantation mixed up with the Growth Charm and it ended up the size of a badger before he could stop it.
Concealment Charm
Used to conceal something so that it cannot be seen.
Confundus Charm
“Confundo�?is Latin for “to confuse�? Used to confuse an object or person, to make them believe what the spell caster wants them to.
Conjunctivitis Curse
Conjunctivitis is an inflammation of the conjunctiva (mucous membrane that lines the surface of the eyelid and the exposed surface of the eyeball), and is taken from the Latin "conjunctus," meaning "joined together."
This curse is aimed at the eyes of the victim and causes the eyelids to crust together so that the victim cannot see. In addition to loss of sight, it seems to cause pain to the victim as well.
Crucio
Latin for “to torture�?
The Cruciatus Curse. This inflicts severe physical pain on whomever it is cast upon. To effectively use the Cruciatus Curse, the witch or wizard casting the spell must have the genuine desire to cause pain. When effectively used, the curse is excruciating and has the ability to drive victims insane. As such, it is one of the three Unforgivable Curses. The use of this spell against another human being is punishable by a life sentence in Azkaban.
Curse Alleviation Charm
When Katie Bell was injured by the cursed necklace from Malfoy, Professor Snape did everything that he could to prevent a rapid spread of the curse. The magic he performed is unknown, and so it is included here simply as a Curse Alleviation Charm.
Curse of the Bogies
Professor Quirrell told his class about this curse, although its exact effect is unknown. Something to do with bogies, no doubt.
Cushioning Charm
Creates an invisible cushioned area. It is primarily used in broomstick manufacture to make the brooms more comfortable to sit on.
Daydream Charm
This gives the spell caster a highly-realistic 30 minute daydream, according to its inventors Fred and George Weasley. Daydream Charms can be found for sale in Weasleys' Wizard Wheezes.
Deletrius
“Delete�?means “to erase�? Used to erase spell images conjured by Priori Incantem.
Densaugeo
From the Latin "dens," meaning "tooth," and "augeo," meaning "increase, enlarge."
Enlarges the teeth of the victim.
Diffindo
Latin for “to split�? A spell that rips an object in half or causes things to separate. It is likely to be the same spell as the Severing Charm. See also "Severing Charm".
Disapparate
From the Latin "disparitio" meaning "disappearance," or "dispareo" meaning "to vanish."
This spell allows the caster to disappear instantly from any given place with a soft popping sound, or alternatively a loud cracking noise. The sound made seems to be different from one spell caster to the next. It is used in conjunction with Apparate. The caster must Disapparate from one location before he or she can Apparate in another.
Disillusion
Literal meaning is to remove an illusion. Generally used to indicate unhappiness with a situation.
Spell used to hide something. Typically used to hide magical objects and occurrences from Muggles.
Dissendium
This is possibly a path-revealing spell. It was used to open a secret passage to Hogsmeade.
Drought Charm
Dries up a limited amount of water. Harry decided he probably wouldn't be able to use it to dry up the entire Hogwarts lake.
Engorgio
“Engorge�?means “to fill to excess�?
The Engorgement Charm. Causes the target to enlarge. See also "Enlargement Charm".
Enlargement Charm
Similar to an Engorgement Charm (Engorgio), this causes an object to swell in size. The Weasley twins put an Enlargement Charm on a copy of The Quibbler which contained Harry's interview, so it may be that the Engorgement Charm works only on organic matter (ie animal or vegetable), whilst the Enlargement Charm works on other objects.
Ennervate
Revives someone, especially someone who has had Stupefy cast on them.
Entrail-Expelling Curse
Invented by Urquhart Rackharrow, 1612-1697. Effect unknown, but presumably involves expelling entrails.
Entrancing Enchantment
Entrances the person the spell is cast upon.
Episkey
From the Greek "episkeyi" meaning "repair". A healing spell. Tonks used to it repair Harry's nose when it was broken by Malfoy on the Hogwarts Express. It may also work on bones, and may therefore have been the spell Lockhart was attempting to cast when he accidentally removed all the bones from Harry's arm.
Evanesco
Latin for “to vanish�?
This spell is used to make an object disappear. It is assumed this spell works only on objects, and not on people.
Expecto Patronum
"Patronus" is Latin for "protector".
The Patronus Charm. When literally translated, the phrase "Expecto Patronum" means, "I expect a guardian." The Patronus Charm is highly advanced magic, beyond Ordinary Wizarding Level. It is used to ward off both dementors and Lethifolds and probably works against other creatures as well. To conjure a Patronus, the spell caster must speak the incantation ("Expecto Patronum") while concentrating hard on an extremely happy thought or memory. When the charm is cast successfully, the spell caster's wand emits a Patronus; a stream of silvery vapor that takes on the shape of an animal. The type of animal the Patronus assumes depends entirely upon the witch or wizard who conjures it, reflecting certain traits of the caster's personality. The Patronus is the embodiment of the caster's happy memories and acts as a shield, protecting the witch or wizard.
Expelliarmus
Latin for “to expel a weapon�?
This spell is used to disarm an opponent. Although a simple spell, it causes the victim's wand to fly out of his or her hand, depriving its victim of his or her primary weapon and means of defense. When used by many people on a single target in tandem, the spell is powerful enough to knock the target off of his or her feet, as was demonstrated on Severus Snape in Harry Potter and the Prisoner of Azkaban.
Extinguishing Spell
Puts out fires. This was used by the keepers of the dragons used in the Triwizard Tournament.
Featherweight Charm
This charm is used to make something lightweight so that it can be carried more easily.
Ferula
Conjures a splint and bandages.
Fidelius Charm
“Fidelis�?is Latin for “faithful friends�?
This is a complex charm that allows someone or something to be hidden away, often times in plain sight, for an indefinite period of time. The location of the hidden people or items is a secret known only to one person, the Secret-Keeper, and the information is stored within their very soul. The Secret-Keeper is the only one with the power to divulge the secret. The information remains undisclosed until said time when the Secret-Keeper decides to reveal it; not even those who have been told the secret information can reveal what they know. However, the Secret-Keeper does not have to directly speak with someone to tell him or her the secret, the information can be disclosed in a letter as long as the Secret-Keeper is the one who wrote it.
Finite
From the Latin “finis,�?meaning “end.�?Similarly to Finite Incantatem, this removes spell effects. It may be that Finite stops a single spell whilst Finite Incantatem stops all current spells. Remus Lupin cast this spell on Neville Longbottom in the Department of Mysteries to remove the effects of a Tarantallegra curse.
Finite Incantatem
From the Latin "finis," meaning "end." Removes the effects of any spells currently cast.
Fire Charm
When Harry and Dumbledore were attacked by Inferi in the Horcrux cave, Dumbledore created a ring of crimson and gold fire to protect them. This may be simple a Dumbledore-powered version of Flagrate or Incendio, or it may be a separate fire creation charm.
Flagrate
“Flagrantia�?is Latin for “burning�? Makes the spell-caster able to draw lines of fire with their wand.
Flame Freezing Charm
Charm used by Medieval witches to remove the effects of the fire when they were burned at the stake. It is a good idea at this point to scream a bit and pretend to be burning.
Flying Charm
Different to Wingardium Leviosa, which merely makes objects float in the air, the Flying Charm allows them to be maneuvered by the user and turns them into genuinely controllable flying items. The Flying Charm is used on broomsticks (as confirmed by Draco Malfoy when he was criticising Ron's broom in 1995 - "why would anyone put a Flying Charm on a mouldy old log like that?" being the words he chose), and also presumably Flying Carpets. It is clear that Flying Charms can be cast only on objects rather than animals or people, as it is well known that no spell yet exists that allows a wizard to fly unaided.
Freezing Charm
Used by Hermione to immobilise Cornish Pixies in Professor Lockhart's first Defence Against the Dark Arts lesson, following Lockhart's pathetic attempt to deal with them himself. Freezing Charms are also effective in disabling Muggle burglar alarms.
Furnunculus
Makes the victim's body break out in boils. When used in conjunction with the Jelly-Legs Jinx it causes tentacles to sprout all over the victim's face.
Gripping Charm
Allows a person to grip an object more effectively. This was invented in 1875 and is primarily used in Quidditch to allow the Chasers to handle the Quaffle one-handed whilst still keeping a grip on their brooms.
Growth Charm
Similar to the Enlargement Charm and the Engorgement Charm, this spell causes the target to increase in size. The precise differences between these three enchantments are unknown. Harry got confused during his Charms OWL and cast a Growth Charm on a rat he was meant to be turning orange. It had grown to the size of a badger before he could stop it.