Jay P. Green’s Classic Bible Dictionary says about the word trinity, "This is not itself a Biblical term, but was a term coined by Tertullian to refer to this whole concept under one word" (p. 483). The Cyclopedia of Biblical, Theological, and Ecclesiastical Literature says forthrightly, "Respecting the manner in which the Father, the Son, and the Holy Spirit make one G-d, the Scripture teaches nothing, since the subject is of such a nature as not to admit of its being explained to us" ("Trinity," p. 553).
This authority is not alone in its insight. Another explains that the whole notion of a Trinity emerged from heated disagreement and dispute: "The doctrine developed gradually over several centuries and through many controversies… The council of Nicaea in 325 stated the crucial formula for that doctrine in its confession that the ‘Son is of the same substance…as the Father,’ even though it said very little about the Holy Spirit…By the end of the 4th century…the doctrine of the Trinity took substantially the form it has maintained ever since" (Encyclopaedia Britannica, Trinity).