The ambiguity is thus expressed by Mr. Robertson Athanasius, Proleg. p. xxxi., in this Series.:  “We may look at a concrete term as denoting either this or that individual simply (τόδε τι), or as expressing its nature, and so as common to more individuals than one.  Now properly (πρώτως) οὐσία is only appropriate to the former purpose.  But it may be employed in a secondary sense to designate the latter, in this sense species and genera are δεύτεραι οὐσίαι, the wider class being less truly οὐσίαι than the former.”  Perhaps the earliest use of οὐσία in Christian writings is in Justin M. Tryph. c. 128*., where he describes the Logos as “having been begotten from the Father, by His power and will, but not by abscission (ἀποτομήν), as if the οὐσία of the Father were divided, as all other things when divided and cut are no longer the same as before.”  His example was fire, from which other fires are kindled, while it remains undiminished and unchanged.  According to Dr. Newman Arians, p. 186., οὐσία here means “substance, or being.”