Full Idea
To ti en einai: essence, what-it-is-to-be
Gist of Idea
To ti en einai: essence, what-it-is-to-be
Source
PG (Db (lexicon) [c.1001 BCE], 88)
A Reaction
This is Aristotle's main term for what we would now call the 'essence'. It is still not a theory of essence, merely an identification of the target. 'Form' is the nearest we get to his actual theory.