I think you may be getting your information from a web site that has
incorrectly linked a Thayer's lexicon discussion of katholikos with
Strong's discussion of katho. The Strong's concordance itself has no
mention katholikos. Thayer's discussion is a bit wider than just NT, and
goes into some of the patristic literature as well.
Blessings,
Jerry Shepherd
Taylor Seminary
Edmonton, Alberta
Jerry Shepherd
jshepherd53 AT gmail.com