A warlock is a male practitioner of witchcraft (distinguished from a wizard or sorcerer, whose magic may be benign). The most commonly accepted etymology derives warlock from the Old English wǣrloga meaning "oathbreaker" or "deceiver".

However, in early modern Scots, the word came to be used as the male equivalent of witch (which can be male or female, but is used predominantly for females). From this use, the word passed into Romantic literature and ultimately 20th-century popular culture. A derivation from the Old Norse varð-lokkur, "caller of spirits", has also been suggested.

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