Abracadabra (Gn.). This symbolic word first occurs in a medical treatise in verse by Samonicus, who flourished in the reign of the Emperor Septimus Seveus. Godfrey Higgins says it is from Abra or Abar “God”, in Celtic, and cad ‘‘holy” ; it was used as a charm, and engraved on Kameas as an amulet. [w.w.w.] Godfrey Higgins was nearly right, as the word “Abracadabra” is a later corruption of the sacred Gnostic term “Abrasax”, the latter itself being a still earlier corruption of a sacred and ancient Coptic or Egyptian word: a magic formula which meant in its symbolism ‘‘Hurt me not”, and addressed the deity in its hieroglyphics as “Father”. It was generally attached to an amulet or charm and worn as a Tat (q.v.), on the breast under the garments.
Source: H.P.Blavatsky - The Theosophical Glossary