The above is another question that arrived via the search terms list.
The term “Trinity” (trinitas in the Latin) was first used to describe the three ‘persons’ of God by Tertullian, a Latin Christian scholar living in the 300s. I should note that the word trinity was not originally meant to be a proper noun but rather a word denoting a relationship in much the same way that the word ‘spouse’ implies marriage.
The word trinity does not itself appear anywhere in Scripture but there are verses such as “The grace of the Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all” (II Cor. 13:14) that list the persons of the Trinity.
Going further back, many Christians believe the Trinity is described in the opening chapters of Genesis: “In the beginning God created the heavens and the earth. Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters.” (1:1-2) This passage includes the Father and the Spirit.
The Son is first mentioned, though not by name, in Genesis 3:15. God says to the serpent: “I will put enmity between you and the woman, and between your offspring and hers; he will crush your head, and you will strike his heel.” Christians believe this is the first promise of the Messiah made in scripture, which was fulfilled by Jesus the Son.