Warlock

Warlock is a very old term that has two meanings: to describe a wizard of unusually fierce appearance or as a title denoting particular skill or achievement. It originally denoted one learned in duelling and all martial magic or given as a title to a wizard who had preformed feats of bravery (as Muggles are sometimes knighted). It is, sometimes, incorrectly used as interchangeable with the term "wizard."

Known warlocks

 * Albus Dumbledore
 * An unidentified Armenian individual
 * Barnabas Deverill
 * Brutus Malfoy (possibly)
 * D.J. Prod
 * Garvin Lügner
 * Jarleth Hobart
 * Perkins
 * Zaccaria Innocenti
 * Ernie Macmillan's ancestor (possibly)

Fictional warlocks

 * The warlock in The Warlock's Hairy Heart

Behind the scenes

 * In The Tales of Beedle the Bard, Albus Dumbledore mentions an old magazine called Warlock at War - this was written by Brutus Malfoy and was essentially concerning the war he felt was between pure-bloods and Muggles. The term here may have been used to draw on the fact that warlocks were skilled in warrior magic, as well as it being used synonymously with wizard.
 * Also in The Tales of Beedle the Bard there is a story called The Warlock's Hairy Heart, which concerns a warlock engaging in dark magic. Dumbledore claims this is to show that he is an accomplished wizard regardless of his darker inclinations.
 * Harry Potter saw some "wild-looking" warlocks in the Leaky Cauldron in 1993.

Etymology
The Anglo-Saxon waerloga or "oathbreaker", which passed through a Middle English form of warloghe or warlach to become warlock, has two components, waer, "covenant", and loga, "betrayal". The latter is derived from leogan "to lie", and may consequently have commonalities with Loge/Loki, the Norse God of Mischief and betrayer of Asgard.

Appearances

 * Harry Potter and the Chamber of Secrets
 * Harry Potter and the Half-Blood Prince
 * Quidditch Through the Ages
 * The Tales of Beedle the Bard
 * Wonderbook: Book of Spells