Caput Draconis: The first password to the Gryffindor tower when Harry arrives at Hogwarts.
Etym: Latin for "dragon's head".
Care of Magical Creatures: An elective class at Hogwarts.
Cauldron Cakes: A type of wizard candy, probably something akin to a cupcake.
Celestina Warbeck: Etym: This was the term for a late-18th-century keyboard instrument developed from the armonica. The word is from Latin caelestis "heavenly".
centaur: A mythical creature with the body of a horse, and the top half of a human attached where the neck would be. Rowling's centaurs are largely peaceful but wish to keep to themselves. A group of them lives in the Forbidden Forest.
Chamber of Secrets: An enormous magical cavern, rumored to have been constructed by Salazar Slytherin, concealed beneath Hogwarts for nearly eight centuries, even when a modern girls' bathroom was built over the entrance, until Tom Riddle figured out how to open it and pin the blame on Hagrid.
Chameleon Ghoul: Mentioned in passing, presumably a type of ghoul with some natural ability to disguise itself.
Chang, Cho: A Ravenclaw, a year ahead of Harry, and Seeker for the Ravenclaw Quidditch team.
Etym: No reliable info.
Charlie Weasley [Charles]:
Etym: From ceorl, Old English for "a man".
Charms: One of the basic subjects that all students at Hogwarts have to study, taught by Professor Flitwick. A general term for all sorts of minor spells of instantaneous effect.
Charm Your Own Cheese: One of Molly Weasley's cookbooks.
Chaser: One of the three players on a Quidditch team who pass the Quaffle between them and attempt to throw it through one of the goal hoops. A goal is worth 10 points.
Cho Chang: Etym: No reliable info on the meaning of the name. It was the family name of a couple of Korean artists of the Yi dynasty.
Chocolate Frogs: A wizard candy, undistinguished except for the line of Famous Witches and Wizards trading cards that come with them.
Christmas pudding: A rich fruit pudding, typically splashed with brandy and set alight just before serving. Hiding a silver coin in it is also traditional.
Chudley Cannons: A professional Quidditch team. Chudley itself appears to be fictional, unless it's an alternate spelling of Chudleigh.
Circe: An enchantress who figures in the Odyssey. She transformed Odysseus's crew into pigs. Featured on a Famous Witches and Wizards trading card.
Cleansweep Five: A type of flying broom.
Clearwater, Penelope (CoS ch. 14): Percy Weasley's girlfriend, a Ravenclaw prefect.
Etym: Pretty much what it looks like, and like her first name, a symbol of purity. Just the girl for Percy...
Cliodna: A druid featured on a Famous Witches and Wizards trading card.
Cokeworth: Location of the Railview Hotel.
Colin Creevey: Etym: Anglicization of Gaelic Cailean, which may be from coileán, meaning "young dog, youth" and by extension "cadet".
Comet Two Sixty: A brand of flying broom.
Committee on Experimental Charms: Part of the Ministry of Magic.
Common Welsh Green: A type of dragon native to the British Isles.
conk: British slang for "nose".
Cornelius Fudge: Etym: St. Cornelius was pope from 251 to 253, and is noted for taking a liberal attitude toward Christians who had renounced their faith under duress. He was succeeded by St. Lucius.
Cornish pixies: Small electric-blue creatures; not terribly dangerous, although they seem to have a talent for vandalism.
Crabbe, Vincent: One of Draco Malfoy's cronies.
Etym: From a nickname for someone with an odd gait, like a crab, or a cantankerous person, as a shortening of crabapple.
Creevey, Colin: A Gryffindor, a year behind Harry; Harry's first papparazzo.
Etym: Anglicized form of Gaelic Ó Craoibhe, from a name meaning "curly(-headed)" or "prolific". Thomas Creevey (1768-1838) was a politician and placeman, remembered because some of his journals and correspondence were published in 1903 and 1905.
Crockford, Doris (PS ch. 5): A particularly effusive fan of Harry's that he met in The Leaky Cauldron.
Etym: From the placename Crockford Bridge; further etymology is uncertain and probably not relevant. Also the name of a London gambling club, and the colloquial designation of a reference work produced by the Anglican Church.
Crookshanks: Hermione's unusually intelligent cat.
Etym: Means "crooked legs".
Spells that injure or impede the target. Some require only a wand and
a quick incantation, but stronger ones require the caster to maintain
line-of-sight and keep up the incantation for the full time of effect. The
terms jinx and hex appear to be equivalent, and are used in curse names
for alliterative effect.
Curses and Countercurses
Curses and Countercurses: A book seen in Diagon Alley.
Curse of the Bogies: Something Professor Quirrell mentioned in class. Bogie has varied meanings.