Walter Martin, in his book, Kingdom of the Cults (page 82), makes the claim that the "triune Godhead" is one of greatest doctrines of the Scriptures. He, in effect, gives the Greek transliteration of Tes Theotetos as meaning "triune Godhead". Thus, evidently, he is claiming that the Greek term transliterated as Tes Theotetos is speaking of the alleged triune God, three persons all whom are equally and wholly the Supreme Being.
Colossians 2:9 - For in him dwelleth all the fulnesse of the Godhead bodily. -- King James VersionThe expression Tes Theotetos occurs only once in the Bible and that is at Colossians 2:9, where the King James Version renders it as "Godhead". The problem with using Tes Theotetos as meaning "Triune Godhead" is that it would mean that there are three persons who are dwelling in the Son bodily: The Father, the Son, and the Holy Spirit. It would have one alleged person of the alleged trinity, the Son, dwelling in the same alleged person of the alleged trinity.
1 Corinthians 4:6 - Now these things, brothers, I have in a figure transferred to myself and Apollos for your sakes, that in us you might learn not to think beyond the things which are written, that none of you be puffed up against one another. -- World English
On page 89 of his book, Martin renders Tes Theotetos as "diety"; the word "diety" as applied to forms of the Hebrew and Greek words for "God/god" could be apply to others than the Supreme Being or a false god. On page 112, he refers to Colossians 2:9 as speaking of Jesus' "full deity." Jesus certainly was given the fullness of deity (mightiness) to do the work that the only true Supreme Being had given him to do (John 17:1,3; Colossians 2:10; Ephesians 1:3,17-23); this does not mean that we need to imagine and assume that Jesus is the Supreme Being, and then futher imagine and assume that Jesus is a person of the Supreme Being.
Trinitarians give a vast array of conflicting theories as how Colossians 2:9 is alleged to be, in some vague way, about their triune God philosophy. Nevertheless, all of these theories have to be formulated by thinking beyond what is actually written, and adding assumptions to, and reading assumptions into, what is actually written. The most common explanation is that it the alleged God the Son who dwells in the human body of the man, Christ Jesus. That is not, however, what is stated, and would conflict with many scriptures, since Jesus, having sacrificed that body to God for sin (Hebrews 10:10), was no longer in the days of his flesh. (Hebrews 5:7) Having discussed these points before, I will not do so again here, but will simply provide links to my earlier studies, as well as some other related studies:
The Fullness of Deity
Mystery of the Godhead?
Jesus Died a Human Being - Raised a Spirit Being
The Hebraic Usage of the Titles for "God"