The word is nowadays applied to anything, speech or action, that’s designed to stop you seeing what the politician or salesman is really up to or what’s actually happening. Pay no attention to the man behind the curtain, Dorothy ...
It is known that the word appeared in the seventeenth century as a mock-Latin formula or incantation used by conjurors. What that formula was and where it came from is less certain.
Thomas Ady wrote in his book of 1655, A Candle in the Dark; or, a Treatise Concerning the Nature of Witches and Witchcraft: “I will speak of one man ... that went about in King James his time ... who called himself, The Kings Majesties most excellent Hocus Pocus, and so was called, because that at the playing of every Trick, he used to say, Hocus pocus, tontus talontus, vade celeriter jubeo, a dark composure of words, to blinde the eyes of the beholders, to make his Trick pass the more currantly without discovery”.
Many people today believe that the phrase originated in a corrupted form of the words of the consecration of the host in the old Latin mass: hoc est (enim) corpus (meum), “this is my body”, an idea that was first aired by John Tillotson, who was Archbishop of Canterbury between 1691 and 1694. But as this was part of an anti-Catholic sermon, it may be taken with a fair-sized pinch of salt. Another possibility, suggested in current Oxford dictionaries, is the nonsense Latin phrase “hax pax max Deus adimax”.
Whatever the source, hocus-pocus was at first a general name for jugglers and conjurers and then—later in the seventeenth century—it became a term for a trick or deception. It’s also the source of another common English word, since at the end of the following century it was contracted to make hoax.
Taken from:
http://www.quinion.com/words/weirdwords/ww-hoc1.htm
I've learnt smething new today too Tam,
chris