There are several senses in which a thing may be said to be, as we pointed out. [Met, Book Z, 1028a9]
there are many senses in which a thing is said to be, but all refer to
one starting-point; some things are said to be because they are substances, others because they are affections of substance, others because they are a process towards substance, or destructions or privations or qualities of substance, or productive or generative of substance, or of things which are relative to substance, or negations of some of these things or of substance itself [Met, Book Gamma, 1003b].
Thus, following Franz Brentano's dissertation : On the Several Senses of Being in Aristotle (1862), page 3 :
The various sorts of being which are here enumerated can be reduced to four kinds:
(1) Being which has no existence whatever outside the understanding
(2) The being of movement and of generation and corruption (process toward
(3) Being which has complete but dependent existence (affections of substance,
qualities, things productive and generative);
(4) The being of the substances (ousia).
And see Cat, 5, 2a13 :
A substance —that which is called a substance most strictly, primarily,
and most of all [protai ousiai (πρῶται οὐσίαι), "primary substances"] — is that which is neither said of a subject nor in a subject, e.g. the individual man or the individual horse.
Substance is from Latin : substantia :
From substāns, present active participle of substō (“stand under; exist”), from sub + stō (“stand”).
See also hypostasis :
From ecclesiastical Latin hypostasis, from Ancient Greek ὑπόστασις (hupóstasis, “sediment, foundation; substance, existence, essence”), from ὑπό (hupó) + στάσις (stásis, “standing”).
And see : John Marenbon, Boethius, Oxford UP (2003), page 71 :
Boethius, however, goes out of his way to link his definition of persona to
an Aristotelian understanding of hupostasis. He is helped by a linguistic accident. In order to explain this, it is useful to introduce a new term — one obviously different from any word Boethius himself uses — for things that
belong to Aristotle’s first category (ousia): I shall accordingly speak of ‘first-category things/individuals/universals’.
The linguistic accident consists in the fact that the usual, Latin translation of hupostasis was substantia. But substantia was also the Latin word used by some, including Boethius himself, as the word for first-category things.
For a linguistic analysis regarding Ancient Greek use of the terms regarding being (εἶναι, οὐσία) see :
For a philosophical analysis, from the point of view of modern formal logic, see :