mor'-ti-fi (Ro 8:13 the King James Version and the English Revised Version, thanatoo, the English Revised Version margin "make to die," and Col 3:5, nekroo, the English Revised Version margin "make dead"): This sense of mortify is obsolete in modern English, and the American Standard Revised Version in both places substitutes "put to death," with great advantage. The context in both passages goes to the heart of Paul's doctrine of the union of the believer with Christ. This union has given the soul a new life, flowing (through the Spirit) from Christ in the heavenly world, so that the remnants of the old corrupt life-principle are now dangerous excrescences. Hence, they are to be destroyed, just as a surgeon removes the remnants of a diseased condition after the reestablishment of healthy circulation. The interpreter must guard against weakening Paul's language into some such phrase as "subdue all that is inconsistent with the highest ideals," for Paul views the union with Christ as an intensely real, quasi-physical relation.
⇒See the definition of mortify in the KJV Dictionary
Burton Scott Easton