Arian Bp. of Cyzicus. A pupil of Aetius, he became Bp. of Cyzicus, probably in 360, but he resigned a few months later. He died in exile at Dakora.
His main work, an Ἀπολογητικóς (known as his ‘First Apology’), is probably the defence of his doctrine which he made at a synod at Constantinople shortly before he resigned. It was answered by Basil of Caesarea. Eunomius issued a rejoinder (his ‘Second Apology’), probably in 378; Gregory of Nyssa's Contra Eunomium (c.382) was a reply to this work. Eunomius taught a single supreme Substance, whose simplicity is opposed to all distinction; he denied that the generation of the Son took place within the Divine Nature, but regarded Him as being immediately produced by the Father, from whom He received the creative power which caused Him to resemble the Father. The most prominent feature of his teaching is its stress on the importance of exactitude of doctrine for the life of faith. His chief importance lies in the reaction of the Cappadocian Fathers, whose doctrines of God and human knowledge of God largely took shape as a critique of his teaching.