Quiddity, or Quidity
Quiddity, Or Quidity (quidditas, from quid, mwhat), a term employed in scholastic philosophy as equivalent to the τὸ τί ῆν εἴναι of Aristotle, and denotes what was subsequently called the substantit form. It is the answer to the question, What is it? — quid est? It is that which distinguishes a thing from other things, and makes it what it is, and not another. It is synonymous with essence, and comprehends both the substance and qualities; for qualities belong to substance, and by qualities substance manifests itself. It is the known essence of a thing, or the complement of all that makes us conceive of anything as we conceive of it as different from ally or every other thing. — Krauth's Fleming, Vocab. of Philosophy, s.v.