The verb κατηχεω has the meaning of inform, instruct, teach as used and listed eight times in scripture (Young's Analytical ConcordanceYAC 3). This is an outgoing process : expressive.
The verb in 2 Thess 2:6 (here used in the nom. sing. masc. part.pres. act. see BAGL 2 ) is κατεχω and has a more inward concept of receptiveness and retaining. It is used nineteen times in scripture and is translated in a variety of ways in the KJV, among them 'hold', 'hold fast', 'keep', 'possess' and 'withhold' (Young's Analytical ConcordanceYAC 3).
It seems to me that this sentence has been misunderstood. That the concept in Paul's mind is thatone of an entity lurking in the midst, restraining himself, not drawing attention (though he be lawless, see context) but eventually his lawlessness cannot be hidden any longer and, in the midst, he is now revealed to have been resident all the time.
- EGNT - Englishman's Greek New testament
- BAGL - Bagster's Anaytical Greek Lexicon
- YAC - Young's Analytical Concordance