'''''Ousia''''' ({{IPAc-en|ˈ|uː|z|i|ə|,_|ˈ|uː|s|i|ə|,_|ˈ|uː|ʒ|ə|,_|ˈ|uː|ʃ|ə}}; {{lang-el|οὐσία}}) is aan [[metaphorical]] andimportant [[philosophical]] and [[theological]] term, originally used in [[Ancient Greek philosophy]], then later in [[Christian theology]]. It was used by various Ancient Greek philosophers, like [[Plato]] and [[Aristotle]], as a primary designation for philosophical concepts of ''[[essence]]'' or ''[[substance theory|substance]]''. In [[contemporary philosophy]], it is analogous to [[English language|English]] concepts of ''[[being]]'' and ''[[ontic]]''. 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]].{{sfn|Athanasopoulos|Schneider|2013|p=}}
The [[Ancient Greek]] term ''Ousia'' was translated in [[Latin]] as ''essentia'' or ''substantia'', and hence in English as ''[[essence]]'' or ''[[Substance theory|substance]]''.<ref>[https://books.google.com/books?id=6CD0IRPg4roC&pg=PA29 Commentary on Aristotle's Physics]</ref>
