Tertius

(third), probably a Roman, was the amanuensis of Paul in writing the Epistle to the Romans. (Romans 16:22) (A.D. 55.)

tertius
tertĭus, a, um, num. ord. adj. [ter], the third. I Adj. : vos duo eritis, atque amica tua erit tecum...

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.
tertius
tertius (1) adj.numord. ter, the third : trīs video sententias ferri: unam . . . alteram . . . ter...

An Elementary Latin Dictionary
Tertius
third ...

Hitchcock's Bible Names Dictionary
Tertius
The third, a Roman Christian whom Paul employed as his amanuensis in writing his epistle to the Roma...

Easton's Bible Dictionary