I heard the tail end of an awful story on the news about someone killing a boy who was thought to be a witch. The OED says that witch meaning "a man who practises witchcraft" is a dialect word only, although that can't be the case as I heard it on national news, and it features in several newspaper reports.
There are two separate entries for the noun "witch" in the OED, one for the masculine meaning, and one for the feminine (defined as "a female magician, sorceress" as the original meaning, although needless to say, it soon pejorates into "a woman supposed to have dealings with the devil or evil spirits" - the male version does not have the equivalent pejorative definition). The first citation for 'witch' the man is c890, so it is a very old word. It comes from the Old English wicca, which was a masculine noun. 'Witch' the woman comes from the feminine version, wicce, and the first citation in the OED is from c1000. The Dictionary says that both words probably derive from the verb 'to witch' (wiccian in Old English), meaning 'to practise sorcery'. Interestingly, Wicca itself only went into the OED in 1993; it is defined as "the practices and religious cult of modern witchcraft".