1. One who practices witchcraft (not neccasarily connected with Wicca).
It is also used to describe those who follow the Wiccan religion, and, in some instances, those who practice any type of magick (Goetic, Herbal, Enochian, etc).
2. A bitter or hateful women. Used in a deragatory sense. A hag, if you will.
3. A less insulting (if there is such a thing) form of call someone a bitch.
Salem, Massachusetts and many other places held several trials for those who were seen as "evil witches." As a result, many innocent people were killed.