The word that’s synonymous with magic actually has an interesting origin, finding its roots back in the 2nd century AD. While the exact origins of the word are still up for debate, one of the oldest records found comes from a Roman sage named Serenus Sommonicus.
Sommonicus was the physician to the Roman emperor Caracalla and would prescribe malaria sufferers to wear amulets containing the word “abracadabra” written in the form of a triangle (see below), as it was his belief that the power of the amulet could make lethal diseases go away. According to Wikipedia, other Roman emperors, including Geta and Alexander Severus, were followers of Sommonicus and may have used the “Abracadabra”.
Abrahadabra is a word that first publicly appeared in The Book of the Law, the central sacred text of Thelema. Its author, Aleister Crowley, described it as “the Word of the Aeon, which signifieth The Great Work accomplished.” This is in reference to his belief that the writing of Liber Legis (another name for “The Book of the Law”) heralded a new Aeon for mankind that was ruled by the god Ra-Hoor-Khuit (a form of Horus). Abrahadabra is, therefore, the “magical formula” of this new age. It is not to be confused with the Word of the Law of the Aeon, which is Thelema, meaning “Will.”
Source : collective-evolution.com