warlock

Origin:

Old English wǣrloga 'traitor, scoundrel, monster', also 'the Devil', from wǣr 'covenant' + an element related to lēogan 'belie, deny'. From its application to the Devil, the word was transferred in Middle English to a person in league with the Devil, and hence a sorcerer. It was chiefly Scots until given wider currency by Sir Walter Scott