ABRACADABRA, a word analogous to Abraxas (q.v.) used as a magical formula by the Gnostics of the sect of Basilides in invoking the aid of beneficent spirits against disease and mis fortune. It is found on Abraxas stones, which were worn as amulets. The Gnostic physician Serenus Sammonicus gave pre cise instructions as to its mystical use in averting or curing agues and fevers generally. Subsequently its use spread beyond the Gnostics, and in modern times it is applied contemptuously to complicated, unscientific hypotheses.