nominal definition

A definition, for example of a species of substance or animal, that locates it by sufficient of its properties to distinguish it from other kinds of substance or animal, but without getting at its underlying structure or ‘essence’. Thus a definition of water as the colourless liquid good for bathing and drinking is a nominal definition; a definition of it as H₂O is a ‘real’ definition. The distinction is first made explicit by Locke, although his own attitude towards the possibility of finding real definitions, specifying the real essences, of things is ambivalent. See essentialism.