Here we find, "The magical spell of common parlance, 'hocus pocus,' derives from the words of consecration in the Latin Mass, “hoc est enim corpus”–this is my very body."
True or false? I don't know. I do know that one ought not believe everything one reads.
Addendum: I was fishing of course, my OED and other relevant reference works being packed away at the moment, and I did indeed quickly snag a juicy morsel from the blogosphere's vasty deeps. The following courtesy of Jonathan Watson:
We have, it seems, at least this from the OED:
hocus-pocus, n., adj., and adv.
Pronunciation: /ˈhəʊkəsˈpəʊkəs/
Forms: hocas pocas, hokos pokos, hokus pokus.
Etymology: Appears early in 17th cent., as the appellation of a juggler (and, apparently, as the assumed name of a particular conjuror) derived from the sham Latin formula employed by him: see below, and compare Grimm, Hokuspokus .
The notion that hocus pocus was a parody of the Latin words used in the Eucharist, rests merely on a conjecture thrown out by Tillotson: see below.
1655 T. Ady Candle in Dark 29, 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.
1694 J. Tillotson Serm. (1742) II. xxvi. 237 In all probability those common juggling words of hocus pocus are nothing else but a corruption of hoc est corpus, by way of ridiculous imitation of the priests of the Church of Rome in their trick of Transubstantiation.