If anyone wants to know where word Trinity comes from I have some information.
In Scripture there is as yet no single term by which the Three Divine Persons are denoted together. The word trias (of which the Latin trinitas is a translation) is first found in Theophilus of Antioch about A.D. 180. He* speaks of "the Trinity of God [the Father], His Word and His Wisdom (“Ad. Autol.”, II, 15*). The term may, of course, have been in use before his time. Afterwards it appears in its Latin form of trinitas in Tertullian (“De pud.” c. xxi). In the next century the word is in general use. It is found in many passages of Origen (“In Ps. xvii”, 15). The first creed in which it appears is that of Origen’s pupil, Gregory Thaumaturgus. In his Ekthesis tes pisteos composed between 260 and 270, he writes:
There is therefore nothing created, nothing subject to another in the Trinity: nor is there anything that has been added as though it once had not existed, but had entered afterwards: therefore the Father has never been without the Son, nor the Son without the Spirit: and this same Trinity is immutable and unalterable forever (P. G., X, 986).
I am still looking for the document that actually have the word “trinitas” in it. Thanks.