Full Idea
To define something just means to set forth its limits in such a way that one can distinguish it from all other things of a different kind. To distinguish it from all other things of the same kind belongs to the theory of 'individuation'.
Gist of Idea
Definition distinguishes one kind from another, and individuation picks out members of the kind
Source
David S. Oderberg (Real Essentialism [2007], 1.4)
Book Reference
Oderberg,David S.: 'Real Essentialism' [Routledge 2009], p.19
A Reaction
I take Aristotle to have included individuation as part of his understanding of definition. Are tigers a kind, or are fierce tigers a kind, and is my tiger one-of-a-kind?