OMOIUSIANS (OMEUSIANS, SEMIARIANS). — They were followers of the Arianizing doctrine, which rejects the consubstantiality of the Son, so as to grant him only a nature similar (ὁμοιούσιος) to that of the Father.
Arianism (v.) did not end with the Council of Nicaea (325), but, through the support first of Constantius and then of Valens, succeeded in remaining strong and threatening, giving rise to three principal heretical currents: those of the Anomoeans, the Homoeans, and the O. The Anomoeans were pure Arians, who maintained precisely that the Son is entirely dissimilar (ἀνόμοιος) from the Father. The Homoeans, little or not at all concerned with doctrinal questions, were content with a vague formula that specified nothing: the Son is like (ὁμοιος) the Father. The O., on the other hand, rejected the consubstantial (ὁμοιούσιος) on the one hand, out of horror of Sabellianism, while on the other they did not feel able to proclaim the Son altogether dissimilar (ἀνόμοιος) from the Father; they therefore taught that the Son is like the Father in all things, including in essence (ὁμοιούσιος). In fact, almost all of them were orthodox as regards the divinity of the Word, and differed from Catholics only in the term ὁμοιούσιος, which they substituted for the ὁμοιούσιος of Nicaea, with the intention of giving due emphasis to the personal distinction, which some strict Nicenes, in the heat of the struggle, had somewhat neglected. St. Athanasius and St. Hilary themselves showed themselves conciliatory toward them. Later, however, a large number of them fell into the Pneumatomachian or Macedonian heresy.