My answer doesn't seem long enough to be rejected, but it hasn't been accepted, so here it is in two parts...
The word first appeared in a poem by the Roman writer, Quintus Severus Sammonicus, during the second century AD. There are various theories as to its origin. It may have come from the Greek, ‘abrasadabra', which was itself a corruption of Abraxas, a god worshipped by the followers of a mystic called Basilides. It may also be related to the mystical Jewish kabbalah, in which the three words ‘ab' = father, ‘ben' = son and ‘Acadsch' = divine spirit...ie Father, Son and Holy Ghost...appear together. That sounds, as ‘abenacadash', quite like ‘abracadabra'.
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