🔼The name Tertius in the Bible
The name Tertius occurs only once in the Bible. Tertius was the scribe who wrote down the words of Paul in what later would be called Paul's Epistle to the Romans (Romans 16:22). Church tradition holds that Tertius started out his Christian career as one of the seventy disciples (Luke 10:1), and after his stint with Paul moved on to Iconium to succeed Sosipater as bishop there.
Probably much more significant is that Paul elaborated on his status of prisoner of the Lord (Ephesians 4:1) possibly also to poetically align his philosophy towards Roman rule with that of Jeremiah (the other famous prisoner of the Lord) towards Babylonian rule. Both men preached non-resistance and compliance and both enemy occupations finally resulted in the destruction of the temple of YHWH. The other famously named scribe in the Bible is Baruch, the scribe of Jeremiah (and a third one is possibly Silvanus; 1 Peter 5:12).
🔼Etymology and meaning of the name Tertius
The name Tertius is the same as the common Latin adjective tertius, meaning Third. Names derived from numerals were quite common in Roman times; authors from that time report of myriads of men named Primus, Secundus, Septimus, Octavian and so on.
Note that right after Tertius announces himself in Paul's letter, the gentlemen make mention of Quartus, meaning Fourth (Romans 16:23). This may not be significant, but very few things in the Bible aren't. Also note that the name Tertullus, belonging to the Roman lawyer who assisted Paul prosecutors, is a diminutive form of Tertius.