What is "nontrinitarianism"

n. The religious belief that rejects the Christian concept of the trinity.

Nontrinitarianism refers to belief systems within Christianity which reject the mainstream Christian doctrine of the Trinity, namely, the teaching that God is three distinct hypostases or persons who are coeternal, coequal, and indivisibly united in one being or ousia. Certain groups emerging during the Protestant Reformation have historically been known as antitrinitarian.

According to churches that consider the decisions of ecumenical councils final, Trinitarianism was definitively declared to be Christian doctrine at the 4th-century ecumenical councils, that of the First Council of Nicaea (325), which declared the full divinity of the Son, and the First Council of Constantinople (381), which declared the divinity of the Holy Spirit.

In terms of number of adherents, nontrinitarian denominations comprise only a small minority of modern Christianity. By far the two largest nontrinitarian denominations are The Church of Jesus Christ of Latter-day Saints ("Mormons") and the Jehovah's Witnesses, though there are a number of other smaller ones, including the Christadelphians, Christian Scientists, Dawn Bible Students, Iglesia ni Cristo, Living Church of God, Oneness Pentecostals, Members Church of God International, Unitarian Universalist Christians, The Way International, The Church of God International and the United Church of God.

Nontrinitarian views differ widely on the nature of God, Jesus, and the Holy Spirit. Various nontrinitarian views, such as Adoptionism, Monarchianism, and Subordinationism existed prior to the formal definition of the Trinity doctrine in A.D. 325, 381, and 431, at the Councils of Nicaea, Constantinople, and Ephesus. Nontrinitarianism was later renewed by Cathars in the 11th through 13th centuries, in the Unitarian movement during the Protestant Reformation, in the Age of Enlightenment of the 18th century, and in some groups arising during the Second Great Awakening of the 19th century.

The Christian doctrine of the Trinity is not present in other major Abrahamic religions. See separate articles discussing the views about this doctrine held by Judaism and Islam.