Warlock

A warlock is a witch who has forsaken their craft. Back in the day they were oath breakers who have betrayed their covens, but nowadays it's associated with those who make deals with demons in order to achieve a malevolent task.
Non-witches practicing witchcraft are also sometimes called warlocks, as they aren't born witches and would have no familiarity with history and ways of a witch.
Non-witches tend to mistakenly liken them as the male counterpart of witches.