Where did the word “Trinity” originate?

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Where did the word “Trinity” originate?

The following excerpt from Basic Thelogy by Charles Ryrie should answer your question.

The early church fathers did not formulate any clear statement concerning the Trinity. Some were unclear about the Logos, and most were unconcerned about giving attention to the Spirit except for His work in the lives of believers. In answer to Praxeus, Tertullian (ca. 165-220) asserted the threeness aspect of God, being the first to use the word Trinity. However, he did not have a full and accurate understanding of the Trinity, his views being tinged with subordinationism. Tertullian was battling Monarchians who opted for the unity of God and denied trinitarianism. Monarchianism existed in two forms.

1. Dynamic Monarchianism (or adoptionism). This was first expounded by Theodotus of Byzantium about 210, and viewed Jesus as a man who was given special power by the Holy Spirit at His baptism.

2. Modalistic Monarchianism. This was more influential, attempting not only to maintain the unity of God but also the full deity of Christ by asserting that the Father became incarnated in the Son. In the West it was known as Patripassianism since the incarnated Father also suffered in the Son; and in the East as Sabellianism after its most famous representative who taught that the Persons in the Godhead were modes in which God manifested Himself. Though Sabellius used the word “Person” he meant it as a role or manifestation of the one divine essence.

No illustration is going to be perfect.

But from the very beginning we see God as a Trinity. Notice the plural pronouns "us" and "our" in Genesis 1:26 -- Then God said, "Let us make man in our image, in our likeness, and let them rule over the fish of the sea and the birds of the air, over the livestock, over all the earth, and over all the creatures that move along the ground."

Though not a complete list, here is some other Scripture that shows God is one, in Trinity:

• "Hear, O Israel! The LORD is our God, the LORD is one!" (Deut. 6:4)
• "I am the LORD, and there is no other; Besides Me there is no God." (Isa. 45:5)
• There is no God but one. (1Cor. 8:4)
• And after being baptized, Jesus went up immediately from the water; and behold, the heavens were opened, and he saw the Spirit of God descending as a dove, and coming upon Him, and behold, a voice out of the heavens, saying, "This is My beloved Son, in whom I am well-pleased." (Matt. 3:16-17)
• "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit." (Matt. 28:19)
• Jesus said: "I and the Father are one." (John 10:30)
• "He who has seen Me has seen the Father." (John 14:9)
• "He who beholds Me beholds the One who sent Me." (John 12:45)
• If anyone does not have the Spirit of Christ, he does not belong to Him. (Rom. 8:9)
• "Joseph, son of David, do not be afraid to take Mary as your wife; for that which has been conceived in her is of the Holy Spirit." (Matt. 1:20)
• And the angel answered and said to her [Mary], "The Holy Spirit will come upon you, and the power of the Most High will overshadow you; and for that reason the holy offspring shall be called the Son of God." (Luke 1:35)
• [Jesus speaking to His disciples] "And I will ask the Father, and He will give you another Helper, that He may be with you forever; the Spirit of truth, whom the world cannot receive, because it does not behold Him or know Him, but you know Him because He abides with you, and will be in you." ... "If anyone loves Me, he will keep My word; and My Father will love him, and We will come to him, and make Our abode with him." (John 14:16-17, 23)