WARLOCK, a wizard, sorcerer or magician (see MAGIC). The word in O. Eng. is wasrloga, literally "a liar against the truth," from war, truth, cognate with Lat. verum (cf. Ger. wahr), and loga, liar, from leogan, to lie (cf. Ger. lilgcn). It was thus used with the meaning of a traitor, deceiver, a breaker of a truce. In M. Eng. it is found as a name for the devil (warloghe), the arch liar and deceiver. The use of the word for a sorcerer or wizard, one whose magic powers are gained by his league with the devil, seems to be a northern English or Scottish use.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)