Theories about the source of the word are:-
Abracadabra - I create as I speak
A possible source is Aramaic: אברא כדברא avra kehdabra which means "I will create as I speak".
Abracadabra - The curse and the pestilence
There is the view that Abracadabra derives from the Hebrew, ha-brachah, meaning "the blessing" (used in this sense as a euphemism for "the curse") and dabra, an Aramaic form of the Hebrew word dever, meaning "pestilence." They point to a similar kabbalistic cure for blindness, in which the name of Shabriri, the demon of blindness, is similarly diminished. Other scholars are skeptical of this origin and claim that the idea of diminishing the power of demons was common throughout the ancient world, and that Abracadabra was simply the name of one such demon.
Abracadabra - Father Son Holy Spirit
Some point to the Hebrew words av ("father"), ben ("son"), and ruakh hakodesh ("the holy spirit").
Abracadabra - Disappear like this word
Some have argued that the term may come from the Aramaic abhadda kedhabhra, meaning 'disappear like this word'. Rather than being used as a curse, the Aramaic phrase is believed to have been used as a means of treating illness.
Abracadabra - Abraxas
It has also been claimed that the word comes from Abraxas, a Gnostic word for God (the source of 365 emanations, apparently the Greek letters for Abraxas add up to 365 when deciphered according to numerological methods). It has also been claimed to come from Abracalan (or Aracalan), said to have been both a Syrian god and a Jewish magical symbol.