|Noah Webster's Dictionary|
1. (n.) Capability of deceiving.
2. (n.) Liability to be deceived or misled; as, the deceivableness of a child.
Int. Standard Bible Encyclopedia
de-sev'-a-b'-l-nes, de-sev' (nasha', "to lead astray"): "The pride of thy heart hath deceived thee" (Jeremiah 49:16), i.e. "Thy stern mountain fastnesses have persuaded thee that thou art impregnable." In Jeremiah 20:7, "O Lord, thou hast deceived me, and I was deceived," pathah, signifies "to be enticed," "persuaded," as in the American Standard Revised Version and the Revised Version, margin.
In the Old Testament most often, and in the New Testament regularly, the various words rendered in the King James Version "deceive" denote some deliberate misleading in the moral or spiritual realm. False prophets (Jeremiah 29:8), false teachers (Ephesians 5:6) and Satan himself (Revelation 12:9) are deceivers in this sense. In the gospels, the King James Version "deceive" (planao, 9 times Matthew 24:4, 5 parallel Mark 13:5, 6 parallel Luke 21:8 Matthew 24:11, 24 John 7:12, 47) becomes in the Revised Version (British and American) "lead astray"; the same change is made in 1 John 2:26; 1 John 3:7; but elsewhere (13 t) both the King James Version and the Revised Version (British and American) render planao by "deceive."
"Deceivableness" (apate), only in 2 Thessalonians 2:10, signifies power to deceive, not liability to deception; the Revised Version (British and American) "deceit."
F. K. Farr
Deceivableness (1 Occurrence)
2 Thessalonians 2:10 And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved. (KJV WBS)