Aristotle

“ The nature and forms of Definition A definition which gives the real nature of a thing also gives its cause, and thus differs only in form from demonstration. There are three classes of definition: (1) An indemonstrable explanation of the essence of a thing; (2) Definitions which resemble a syllogism concerning a thing’s essence; (3) A conclusion of an essential demonstration. Since definition is, as we have said, the expression of a thing’s essence, it is clear that one kind of definition may give the meaning of the name, or of some other expression having the force of a name:—e.g. ”