The magic word 'Abracadabra' has been around a very long time. However, its meaning and origins are uncertain. this doesn't stop anybody speculating on them, though.
Whet we do know is that it appears in the Second century CE in a poem called Praecepta de Medicina in Liber medicinalis, a medical textbook possibly written by Quintus Serenus Sammonicus who may have been the doctor of emperor Septimus Severus. But the book does mention abracadabra as a healing charm, worn round the neck of a sick person and discarded after 9 days.
The word seems to have been fairly popular and survived, written in "word triangles", in charms used throughout the middle ages and possibly even as late as the Plague of 1665.
In the 19th Century, 'abracadabra' was occasionally used as an adjective to mean fake or charlatan. Today, it is an all purpose magic word for use by amateur and professional conjurers alike, as a way of building dramatic tension or distracting the audience.
Well, possible is a funny word, but here are some of the suggested origins of 'abracadabra'. Some are more plausible than others.
Options from Hebrew / Aramaic
Partly because of its supposed Gnostic origins, and also the sound of the word, it has often been thought or suggested that 'abracadabra' is a Hebrew term of some kind. However, to a Hebrew speaker 'abracadabra' sounds Aramaic, as it's full of 'a' sounds. some suggestions of its meaning are:
One major argument against all of these is that 'abracadabra' is the anglicization of the original word, which had a soft 'c' sound (via French) and was in the original form something like "abraSadabra".
Other possible origins
The most common non-Hebrew/Aramaic origin suggested for 'abracadabra' is that is some form of the Greek name Abacax or Abraxas. This was a Gnostic name of God, especially used by the Egyptian Basilideans. The gematria of this name is 365 and it was believed to hold power.
Another theory is that it is a word a bit like "Alphabet", made up from the first four letters in Phonecian: "A, Bra, Ca, Da". This is a bit dodgy too, as the third Phonecian letter was probably a 'g'-sound, like Gimmel and Gamma.
In conclusion, 'abracadabra' has been around so long nobody can remember where it comes from. But it's a funny word. Say it to yourself four times, and you'll see what I mean.
The Oxford English Dictionary (online)