Ousia

Ousia (/ˈuːziə, ˈuːsiə, ˈuːʒə, ˈuːʃə/; Ancient Greek: οὐσία) is a philosophical and theological term, originally used in ancient Greek philosophy, then later in Christian theology. It was used by various ancient Greek philosophers, especially Aristotle, as a primary designation for philosophical concepts of essence or substance. It is analogous to concepts of being and the ontological in contemporary philosophy. In Christian theology, the concept of θεία ουσία (divine essence) is one of the most important doctrinal concepts, central to the development of trinitarian doctrine.

The Ancient Greek term θεία ουσία (theia ousia; divine essence) was translated in Latin as essentia or substantia, and hence in English as essence or substance.