The most commonly accepted etymology derives warlock from the Old Englishwǣrloga meaning "oathbreaker" or "deceiver". 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 Norsevarð-lokkur, "caller of spirits", has also been suggested, but the OED considers this implausible due to the extreme rarity of the Norse word and because forms without hard -k, which are consistent with the Old English etymology (“traitor”), are attested earlier than forms with a -k.
^McNeill, F. Marian (1957). The Silver Bough: A Four Volume Study of the National and Local Festivals of Scotland. 1. Glasgow: William Maclellan.
^Chambers, Robert (1861). Domestic Annals of Scotland. Edinburgh.
^Sinclair, George (1871). Satan's Invisible World Discovered. Edinburgh.
^Cleasby, R.; Vigfusson, G. (1874). An Icelandic-English Dictionary. London: Macmillan.
^Olsen, M. (1916). Maal Og Minne. Oslo: Bymalslaget.
^Loewe, M.; Blacker, C. (1981). Oracles and Divination. London: George Allen & Unwin. p. 130. 'Vardlokkur'...is related to the Scots dialect word 'warlock', wizard, and the meaning is thought to relate to the power to shut in or enclose"
^Thomas Thomson, A History of the Scottish People from the Earliest Times (1896), page 286: "Where one man suffered as a warlock, ten women at least were executed as witches."
^Robert Chambers, Domestic Annals of Scotland: From the Reformation to the Revolution (1874), page 244
^Journal of Jurisprudence and Scottish Law Magazine (1891), Execution of the Judgment of Death, page 397: "We read (Law's Memor. Pref. lix.) that 'one John Brugh, a notorious warlock (wizard) in the parochin of Fossoquhy, by the space of thirty-six years, was worried at a stake and burned, 1643.'"
^Roger A. Mason, Scots and Britons: Scottish Political Thought and the Union of 1603 (2006, ISBN0521026202), page 199
^Julian Havil, John Napier: Life, Logarithms, and Legacy (2014, ISBN1400852188), page 19