in ecclesiastical history, the name of several sects of heretics; some of whom maintained, that the Son was only a similar, not the same, substance with the Father; and others, that he was not only a distinct, but a dissimilar substance. Two of these sects had their denomination from Acacius bishop of Cesarea, who lived in the fourth century, and changed his opinions, so as, at different times, to be head of both. Another was named from Acacius patriarch of Constantinople, who lived in the close of the fifth century.