Ousia

Ousia (/ˈuːziə, ˈuːsiə, ˈuːʒə, ˈuːʃə/; Greek: οὐσία) is analogous to the English concepts of being and ontic used in contemporary philosophy. Ousia is often translated (sometimes incorrectly) to Latin as substantia and essentia, and to English as substance and essence; and (loosely) also as (contextually) the Latin word accident (sumbebekós).

οὐσία is the ancient Greek noun formed on the feminine present participle of the verb , eimí, i.e. "to be, I am",

Aristotle defined protai ousiai, or “primary substances”, in the Categories as that which is neither said of nor in any subject, e.g., “this human” in particular, or “this ox”. The genera in biology and other natural kinds are substances in a secondary sense, as universals, formally defined by the essential qualities of the primary substances; i.e., the individual members of those kinds.

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