The Collaborative International Dictionary
Monoousian
Monoousian \Mon`o*ou"si*an\, Monoousious \Mon`o*ou"si*ous\, a. [Mono- + Gr. ? being, substance, essence.] (Theil.) Having but one and the same nature or essence.
Wiktionary
monoousian
a. (context theology English) Having one and the same nature or essence, especially with regard to the persons of the Trinity.