Anomoeanism was the belief of a sect of radical Arians of the mid fourth century who asserted that Jesus of Nazareth (the Son) was of a different nature and in no way like to that of God (the Father). They believed they followed the original opinions of Arius and rejected his later confessions that he adopted in order to be gain re-admittence into the Church. The sect existed for less than fifty years.
The word Anomœan comes from Greek ἀ(ν)- 'not' and ὅμοιος 'similar', thus, "different; dissimilar; not similar". Also known as heterousianism, which is derived from the Greek, ἑτεροούσιος, heterooúsios, "differing in substance" from ἕτερος, héteros, "another" and οὐσία, ousía, "substance, being".
In mid fourth century, during the reign of Emperor Constantius II, Anomœan was the name by which the followers of Aëtius and Eunomius were distinguished as a theological party. They not only denied the consubstantiality of Jesus, that is, there was a clear distinction between God and Christ, but asserted that he was of a nature different from that of God. This was in contradistinction to the semi-Arians, who also denied the consubstantiality of Jesus, but believed at the same time that he was like the Father.
The semi-Arians condemned the Anomœans in the Council of Seleucia in 359, and the Anomœans condemned the semi-Arians in their turn in the Councils of 361 in Constantinople and Antioch, erased the word ὁμοίος out of the formula of the earlier Council of Rimini, and that of Constantinople, and protested that the Word had not only a different substance, but also a will different from that of the Father. Whence they were to be called Ἀνομοίοι.