OMOIUISIANI (OMEUSIANI, SEMIRIANI). - They were followers of an Arian-leaning doctrine that rejected the consubstantiality of the Son, granting Him only a nature similar (ὁμοιοσύσιος) to that of the Father.
Arianism (v.) did not end with the Council of Nicaea (325), but through the support first of Constantius and later of Valens, it managed to remain strong and threatening, giving rise to three main heretical currents: that of the Anomeans, the Homeans, and the Omoiuisianis. The Anomeans were pure Arians, who maintained that the Son is in all respects unlike (ἀνόμοιος) the Father. The Homeans, little or not at all concerned with doctrinal questions, were content with a vague formula that clarified nothing: the Son is like (ὁμοιος) the Father. The Omoiuisianis, on the other hand, while not accepting the term "consubstantial" (ὁμοιοσύσιος) out of horror of Sabellianism, did not feel able to proclaim the Son utterly unlike (ἀνόμοιος) the Father; they therefore taught that the Son is like the Father in all things, including essence (ὁμοιοσύσιος). In essence, they were almost all orthodox with regard to the divinity of the Word, differing from Catholics only in their substitution of the term ὁμοιοσύσιος for the ὁμοιοσύσιος of Nicaea, with the intention of emphasizing the personal distinction, which some pure Nicenes, in the heat of the struggle, had somewhat neglected. Even St. Athanasius and St. Hilary showed themselves conciliatory toward them. Later, however, a great number of them fell into the heresy of Pneumatomachianism or Macedonianism.