Page 239, Subheading: “The Historical Development of the Doctrine,” Chapter 12, “The Doctrine of the Trinity,” Section 2: “Christian Theology,” in the Book: “Christian Theology : An Introduction,” By Alister E. McGrath, Welley-Blackwell, 5th Edition, 2011.

...The theologian who may be argued to have been responsible for the development of the distinctive trinitarian terminology is Tertullian (c. 160-225). According to one analysis, Tertullian ( coined ) 509 new nouns, 284 new adjectives, and 161 new verbs in the Latin language.[…] Trinitas. Tertullian ( invented ) the word: “Trinity” (Trinitas), which has become so characteristic a feature of Christian theology since his time...”

TERTULLIAN OF CARTHAGE (circa.145-225 C.E.): “...This one, in the meantime, has been the recipient of the gift from the Father, which he has poured forth, the Spirit of Holiness, the third name of the Divinity, and the third stage of the Divine Majesty, the Preacher [= Montanus] of a unified monarchy, in fact it's Interpreter, [= Montanus] even by means of it's economy, for anyone who will permit admittance to the sermons of HIS [= Montanus] NEW PROPHECY, even the guide [Or: “leader”] of all truth, [= Montanus] which consists in the Father, and the Son, and the Holy Spirit, that comes [Or: “follows”] after the Christian sacrament [Or: “sacred oath of allegiance” = Montantist oath]...” - (Chapter 30, Section 5, “Adversus Praxaen,” or “Against Praxaes,” Translated by Matt13weedhacker 18/07/2014)