Trinity - Etymology

Etymology

The English word Trinity is derived from Latin Trinitas, meaning "the number three, a triad". This abstract noun is formed from the adjective trinus (three each, threefold, triple), as the word unitas is the abstract noun formed from unus (one).

The corresponding word in Greek is Τριάς, meaning "a set of three" or "the number three".

The first recorded use of this Greek word in Christian theology (though not about the Divine Trinity) was by Theophilus of Antioch in about 170. He wrote:

"In like manner also the three days which were before the luminaries, are types of the Trinity, of God, and His Word, and His wisdom. And the fourth is the type of man, who needs light, that so there may be God, the Word, wisdom, man."

Tertullian, a Latin theologian who wrote in the early 3rd century, is credited with using the words "Trinity", "person" and "substance" to explain that the Father, Son, and Holy Spirit are "one in essence—not one in Person".

About a century later, in 325, the First Council of Nicaea established the doctrine of the Trinity as orthodoxy and adopted the Nicene Creed, which described Christ as "God of God, Light of Light, very God of very God, begotten, not made, being of one substance with the Father".