The doctrine of the Trinity in the godhead includes the three following particulars, viz. (a) There is only one God, one divine nature; (b) but in this divine nature there is the distinction of Father, Son, and Holy Ghost, as three (subjects or persons); and (c) these three-have equally, and in common with one another, the nature and perfection of supreme divinity. It was the custom in former times for theologians to blend their own speculations and those of others with the statement of the Bible doctrine. It is customary now to exhibit first the simple doctrine of the Bible, and afterwards, in a separate part, the speculations of the learned respecting it. (from McClintock and Strong Encyclopedia, Electronic Database. Copyright © 2000, 2003, 2005, 2006 by Biblesoft, Inc. All rights reserved.)
TRINITY The coexistence of the Father, the Son, and the Holy Spirit in the unity of the Godhead (divine nature or essence). The doctrine of the trinity means that within the being and activity of the one God there are three distinct persons: Father, Son, and Holy Spirit. Although the word trinity does not appear in the Bible, the “trinitarian formula” is mentioned in the Great Commission (Matt 28:19) and in the benediction of the apostle Paul’s Second Epistle to the Corinthians (2 Cor 13:14). (from Nelson’s Illustrated Bible Dictionary, Copyright © 1986, Thomas Nelson Publishers)
Trinity used to express the doctrine of the unity of God as subsisting in three distinct Persons. This word is derived from the Gr. trias , first used by Theophilus (A.D. 168 A.D. - 183 A.D.), or from the Lat. trinitas, first used by Tertullian (A.D. 220 A.D.), to express this doctrine. The propositions involved in the doctrine are these: 1. That God is one, and that there is but one God (Deut 6:4; 1 Kings 8:60; Isa 44:6; Mark 12:29,32; John 10:30). 2.
That the Father is a distinct divine Person (hypostasis, subsistentia, persona, suppositum intellectuale), distinct from the Son and the Holy Spirit. 3. That Jesus Christ was truly God, and yet was a Person distinct from the Father and the Holy Spirit. 4. That the Holy Spirit is also a distinct divine Person. (from Easton’s Bible Dictionary, PC Study Bible formatted electronic database Copyright © 2003, 2006 Biblesoft, Inc. All rights reserved.)