Full Idea
The name 'gold' signifies not only what he who pronounces it knows about it, for example, something very heavy and yellow, but also what he does not know, and that another can know about it, its internal constitution from which colour and weight flow.
Gist of Idea
The word 'gold' means a hidden constitution known to experts, and not just its appearances
Source
Gottfried Leibniz (New Essays on Human Understanding [1704], 6.6.354), quoted by Nicholas Jolley - Leibniz and Locke on Essences
Book Reference
'Leibniz: Critical and Interpretive Essays', ed/tr. Hooker,Michael [Manchester 1982], p.201
A Reaction
Leibniz goes on to use the word 'expert'. This isn't just a hint of Putnam's externalism about concepts like 'water' - it is a clear spelling out of the full idea. Locke would have been astounded by 'atomic number 79', and Leibniz would be, like, 'yeah'.