From exorkizo; one that binds by an oath (or spell), i.e. (by implication) an "exorcist" (conjurer) -- exorcist.
see GREEK exorkizo
1. he who exacts an oath of another.
2. an exorcist, i. e. one who employs a formula of conjuration for expelling demons: Acts 19:13. (Josephus, Antiquities 8, 2, 5; Lucian, epigr. in Anthol. 11,427; often in the church Fathers.)