The concept of the "witch" can be found in EVERY world culture and language in some form or another. Be it kahuna, hexe, strega, bruja, baobh, bacularia or makhsheyfe; the thought that lies behind it is still the same.

So -- Where did the word come from?
What does it exactly mean? -and-
How did it become such a universal principle?

Etymology
Etymology traces the development of a word-form from its earliest recorded occurrence in a language to the present day. Because language is a living entity, words, spellings and meanings are constantly changing. This means that the history of a word and its possible etymology *may not* necessarily coincide. However, I included it in my notes because many people will use etymology as a definitive factor in their arguments for the origins of the witch and witchcraft.

—WITCH—

Word's Origin
Personally, I don't think it really matters where the word 'witch' came from; after all, there is no finite way to prove or disprove its origins. Besides, I am far more interested in where the word is going, than where its' been. If you are interested in the etymology of the word "witch", visit my research page on Etymology.

witch [1] n. -es [ME wyche, from OE wice, wic; probably akin to OE wïcan to yield, give way-more at weak]: any of several trees having pliant branches.
[2] n. -es [ME wicche, from OE wicca, masculine, wizard and wicce feminine, witch; akin to OE wiccian to practice witchcraft, MHG wicken to bewitch, to divine, OE wigle divination, wiglian to divine, wïg idol, image ON yé temple -- more at victim] 1.a dialect British : Wizard, Sorcerer b.(1) : a woman practicing the black arts: sorceress <Halloween ~on a broomstick> <heard of one old ~changing herself into a pigeon -John Rhys> (2) : an ugly old woman : crone, hag <a skinny old ~ with a face like a meat ax and a voice like a buzz saw --Helen Eustis> c. (1) : one supposed to possess supernatural powers especially by compact with the devil or a familiar (2) : a magic spell : hex <it's my idea...he put the ~es on it -Helen Rich> d. or witcher -s: dowser 2 : one that bewitches <the quaint ~ memory -P.B. Shelley>; specifically : a particularly charming or alluring woman 3.a (1) : storm petrel (2) : grebe (3) or witch bird : animal b. also witch flounder: a small mouth blackish or brownish deep water flounder (Glyptocephalus cynoglossus) of the north Atlantic that is of some importance as a food dish c : witch moth.
[3] adjective : of , relating to, or used against witches <~cult> <~ doors used to ward off evil spirits>
[4] verb -ed /-ing/-es [ME wicchen, from OE wiccian to practice witchcraft] 1: bewitch 2 : dowse. [1]

Definitions and Meanings
Definitions are formed by how society utilizes the word in its culture and as cultures change so does its utlization. The question then is: what does it exactly mean to be a witch in our culture? According to many dictionaries, 'witch' in its noun form can refer to a plant, animal or person. Yet --it is the definitions pertaining to the person that is so dominant and so controversial in our society. So, how does our society use the word witch today?

• Generic It simply states: a witch is a person who practices sorcery. Sorcery can include a variety of aspects such as healing, divination, magic, alchemy, necromancy, spells, herbs, meditation, etc. These practices are often an avenue within an established spiritual structure. It is the Generic interpretation that is the common link among the cultures worldwide.

  How did it become such a universal principle? The reason(s) could have been: (a) synchronicity, (b) a single ancient religion, (c) cultural diffusion, or (d) just inherent human nature. --the need to explain the natural world and its inner workings.[2] Personally I think it is the combination of diffusion and inherent human nature. I strongly doubt the synchronicity and the single ancient religion theory.

• Christian A witch is a person who practices the black arts and possesses supernatural powers due to a pact with the devil -also known as Satan. The origins of this definition came from the medieval period circa 1500 when it also included heretics, eccentrics, lepers, Jews and anyone else who didn't conform to the Christian Church. During this time 'witch' almost always referred to women and is evident with words like hag and crone. The reasoning behind this was that women were considered the weaker sex and thus were easily tempted by the devil. Even today, when we think of a witch we think in terms of female, although they can be male as well. Other monotheistic religions like Judaism and Islam also had similar viewpoints.

Notes
1. Webster's Third New International Dictionary of the English Language Volume III
2. A History of Witchcraft—Jeffrey B. Russell; p. 24.

Encyclopedia of Occultism & Parapsychology 4^th ed. Vol.2
Drawing Down the Moon, —Margot Adler