Arianism

A Christian theological doctrine that holds the Son of God was created by the Father and is not coeternal or equal in divinity with him.

Trinity: The Christian doctrine that God is one being in three persons: Father, Son, and Holy Spirit. Arianism challenges the full divinity and coeternity of the Son within this doctrine.
Arius of Alexandria: A Christian presbyter whose teachings about the Son’s created status gave Arianism its name. His preaching in Alexandria triggered the controversy that the doctrine names.
Nicene Christianity: Christian teaching that affirms the Son as eternally divine and of the same substance as the Father. It became the principal doctrinal alternative to Arianism.
Arian controversy: The prolonged fourth-century Christian conflict over the Son’s relation to the Father. Arianism was the central teaching debated across councils, churches, and imperial courts.
Nicene Creed: A Christian creed affirming the Son’s full divinity and eternal relation to the Father. Its wording directly rejects the claim that the Son was created.
Council of Nicaea: A council of Christian bishops convened by Constantine in 325 to address the Arian controversy and other disputes. It condemned Arius’s teaching and affirmed that the Son is of one substance with the Father.
Homoiousianism: A fourth-century Christian position describing the Son as of similar, rather than identical, substance to the Father. It rejected Arius’s strongest claims while avoiding the Nicene term “same substance.”
Homoian Christianity: A fourth-century Christian tradition that described the Son as like the Father without defining their substance. Its influence under several emperors shows that Nicene victory was neither immediate nor inevitable.
Homoousion: The theological term meaning “of the same substance,” used to describe the Son’s relation to the Father. This term became the Nicene counter to Arian distinctions between Father and Son.
Alexander of Alexandria: The bishop of Alexandria who opposed Arius and helped bring the dispute before the wider church. His conflict with Arius turned a local theological disagreement into a major church controversy.

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