Full Idea
What it is to be (pure) water is to be explained in terms of being composed of H2O molecules, but this is not what the word 'water' means.
Gist of Idea
The molecules may explain the water, but they are not what 'water' means
Source
Bob Hale (Necessary Beings [2013], 11.2)
Book Reference
Hale,Bob: 'Necessary Beings' [OUP 2013], p.251
A Reaction
Hale says when the real and verbal definitions match, we can know the essence a priori. If they come apart, presumably we need a posteriori research. Interesting. It is certainly dubious to say a stuff-word means its chemical composition.