Full Idea
There is an application of that old chestnut of the cynic Antisthenes' followers (and other buffoons of that kind). Their claim was that a definition of what something is is impossible. You cannot define silver, though you can say it is like tin.
Gist of Idea
Some fools think you cannot define anything, but only say what it is like
Source
report of Antisthenes (Ath) (fragments/reports [c.405 BCE]) by Aristotle - Metaphysics 1043b
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.241