homoiousian (adj.)

1680s, "having a similar nature," from Greek homoiousios "of the same essence," from homos "one and the same" (see homo- (1)) + ousia "essence," from on, genitive ontos, present participle of einai "to be" (from PIE root *es- "to be"). As a noun from 1732 in reference to the followers of the semi-Arian Eusebius, "who maintained that the nature of Christ is similar to, but not the same with, that of the father" [Century Dictionary].