 John Locke distinguished, in his Essay, “real essence” from “nominal essence.” Nominal essence, according to Locke, is the “abstract Idea to which the Name is annexed (III.vi.2).” Thus, the nominal essence of the name ‘gold’, Locke said, “is that complex Idea the word Gold stands for, let it be, for instance, a Body yellow, of a certain weight, malleable, fusible, and fixed.” In contrast, the real essence of gold is “the constitution of the insensible parts of that Body, on which those Qualities [mentioned in the nominal essence] and all other Properties of Gold depend (III.vi.2).” A rough way of marking the distinction between real and nominal definitions is to say, following Locke, that the former states real essence, while the latter states nominal essence. The chemist aims at real definition, whereas the lexicographer aims at nominal definition.