Theory of Forms
The ancient Greek word for "form" was ("morphe"; cf. morph) and also εἶδος ("eidos") "kind, idea, shape, set", the latter word was famously used in a technical philosophical sense by Plato (and later Aristotle) to denote the ideal identity or essence of something (see Theory of Forms). 'Eidos' can also be associated with thought, proposition, or even concept.